ionospheric disturbances of the 2007 bengkulu and the 2005 nias earthquakes sumatra observed with a regional gps network 1 we studied ionospheric disturbances associated with the two large earthquakes in sumatra indonesia namely the 2007 bengkulu and the 2005 nias earthquakes by measuring the total electron contents tec using a regional network of global positioning system gps receivers we first focus on coseismic ionospheric disturbances cids of the bengkulu earthquake mw 8 5 they appeared 11 16 min after the earthquake and propagated northward as fast as 0 7 km s consistent with the sound speed at the ionospheric f layer height resonant oscillation of tec with a frequency of 5 mhz continued for at least 30 min after the earthquake the largest aftershock mw 7 9 also showed clear cids similar to the main shock a cid propagating with the rayleigh wave velocity was not observed possibly because the station distribution did not favor the radiation pattern of the surface waves this earthquake which occurred during a period of quiet geomagnetic activity also showed clear preseismic tec anomalies similar to those before the 2011 tohoku oki earthquake the positive and negative anomalies started 30 60 min before the earthquake to the north and the south of the fault region respectively on the other hand we did not find any long term tec anomalies within 4 5d ays before the earthquake co and preseismic ionospheric anomalies of the 2005 nias earthquake mw 8 6 were however masked by strong plasma bubble signatures and we could not even discuss the presence or absence of cids and preseismic tec changes for this earthquake

comparative lahar hazard mapping at volcan citlaltepetl mexico using srtm aster and dted 1 digital topographic data abstract in this study we evaluated and compared the utility of spaceborne srtm and aster dems with baseline dted 1 bald earth topography for mapping lahar inundation hazards from volcan citlaltepetl mexico a volcano which has had a history of producing debris flows of various extents in particular we tested the utility of these topographic datasets for resolving ancient valley filling deposits exposed around the flanks of the volcano for determining their magnitude using paleohydrologic methods and for forecasting their inundation limits in the future we also use the three datasets as inputs to a gis stream inundation flow model laharz and compare the results in general all three datasets with spatial resolution of 90 m or better were capable of resolving debris flow and lahar deposits at least 3 106 m3 in volume or larger canopy and slope related height errors in the aster and srtm dems limit their utility for measuring valley filling cross sectional area and deriving flow magnitude for the smallest deposits using a cross sectional area to volume scaling equation height errors in the aster and srtm dems also causes problems in resolving stream valley hydrography which controls lahar flow paths and stream valley morphology which controls lahar filling capacity however both of the two spaceborne dem datasets are better than dted 1 at resolving fine details in stream hydrography and erosional morphologies of volcaniclastics preserved in the valleys around the more humid eastern flanks of the volcanic range the results of laharz flow inundation modeling using all three dems as inputs are remarkably similar and co validate one another for example at citlaltepetl all lahar simulations show that the city of orizaba is the most vulnerable to flows similar in magnitude to or larger than one that occurred in 1920 many of the other cities and towns illustrated are built higher up on terrace deposits of older debris flows and are safe from all but the largest flows which occur less frequently finally asters 60 km swath width and 8 duty cycle presents a challenge for mapping lahar inundation hazards at e w oriented stream valleys in low latitude areas with persistent cloud cover however its continued operations enhances its utility as a means for updating the continuous but one time coverage of srtm and for filling voids in the srtm dataset such as those that occur along steep sided valleys prone to hazards from future lahars

on the causes of biased estimates of seismic moment for earthquakes in central asia 1 comparisons of seismic moment m0 in harvard s centroid moment tensor cmt catalog with m0 estimated from regional surface waves reveal a systematic discrepancy of about a factor of 2 for earthquakes located in western china causes of the discrepancy are investigated with analyses of observations and with calculations of green s function responses for relevant earth models the prem model used in cmt inversions is characterized by a thin high velocity crust unlike tectonic structures in western china while asia used for modeling surface waves was developed for this region analyses of teleseismic body wave synthetics for models similar to prem and asia show that medium properties source radiation patterns and the presence of interfering phases introduce systematic amplitude variations inversions of synthetic data were carried out to simulate features of observed m0 residuals log m0 reg m0 cmt which are 1 a bias of 0 24 0 04 log units for dip slip events with mb 6 to 6 8 2 a tendency for bias to increase with decreasing mb and 3 a mechanism dependence where residuals are large for high angle dip slip events and small for vertical strike slip events residuals for small events scatter more probably due to larger errors in source depth and mechanism affecting both m0 estimates results of inverting synthetics mimic magnitude and mechanism dependences but underestimate the bias in feature 1 rather than impugn the integrity of cmt catalogs this study sheds light on uncertainties introduced by limitations of the methodology

very short term earthquake precursors from gps signal interference based on the 2013 nantou and rueisuei earthquakes taiwan abstract we set up a gps network with 17 continuous gps cgps stations in southwestern taiwan to monitor real time crustal deformation we found that systematic perturbations in gps signals occurred just a few minutes prior to the 2013 nantou ml 6 5 and rueisuei ml 6 4 earthquakes in taiwan the anomalous pseudorange readings were several millimeters higher or lower than those in the background time period these systematic anomalies were found as a result of interference of gps l band signals by electromagnetic emissions ems prior to the mainshocks the ems may occur in the form of harmonic or ultra wide band radiation and can be generated during the formation of mode i cracks at the final stage of earthquake nucleation we estimated the directivity of the likely em sources by calculating the inner product of the position vector from a gps station to a given satellite and the vector of anomalous ground motions recorded by the gps the results showed that the predominant inner product generally occurred when the satellite was in the direction either toward or away from the epicenter with respect to the gps network our findings suggest that the gps network may serve as a powerful tool to detect very short term earthquake precursors and presumably to locate a large earthquake before it occurs nevertheless a direct measurement of ems at the site of the gps array is required in future studies to confirm this hypothesis

the 1997 and 2001 lahars of popocatepetl volcano central mexico textural and sedimentological constraints on their origin and hazards abstract popocatepetl volcano is the most active volcano in central mexico and represents a high risk for more than 40 million people including mexico city in 1994 volcanic activity at popocatepetl renewed with the formation of ash rich plumes up to 7 km high in april 1996 lava emissions filled the crater and were accompanied by a series of explosions that produced eruptive columns up to 8 km high associated with explosive events in 1997 and 2001 two major lahars events occurred leaving debris flow deposits along huiloac gorge for as far as 15 km to the town of santiago xalitzinta the 1997 debris flow deposit originated after a prolonged emission of ash which caused glacier melt and a rapid release of water 1 107 m3 the amount of melting water was sufficient to gradually erode the river bed causing a flood that gradually transformed from a debris flow to a hyperconcentrated flow in contrast the 2001 debris flow that originated from a post depositional remobilization of a pumice flow deposit did not experience any flow transformation and carried 25 water at maximum the different behavior of these two lahars has important hazard implications both lahars reached xalitzintla town but at that point the 1997 lahar had already transformed into a sediment loaded stream flow the 2001 lahar by contrast maintained the characteristics of a debris flow being more competent and with greater destructive power what happened with these lahars demonstrates how important it is to take into consideration secondary volcanic phenomena even though they were not large flows they were capable of threatening populated areas even during periods of volcanic quiescence or reduced magmatic activity

volcanic hazard zonation of the nevado de toluca volcano mexico abstract the nevado de toluca is a quiescent volcano located 20 km southwest of the city of toluca and 70 km west of mexico city it has been quiescent since its last eruptive activity dated at 3 3 ka bp during the pleistocene and holocene it experienced several eruptive phases including five dome collapses with the emplacement of block and ash flows and four plinian eruptions including the 10 5 ka bp plinian eruption that deposited more than 10 cm of sand sized pumice in the area occupied today by mexico city a detailed geological map coupled with computer simulations flow3d titan2d laharz and hazmap softwares were used to produce the volcanic hazard assessment based on the final hazard zonation the northern and eastern sectors of nevado de toluca would be affected by a greater number of phenomena in case of reappraisal activity block and ash flows will affect deep ravines up to a distance of 15 km and associated ash clouds could blanket the toluca basin whereas ash falls from plinian events will have catastrophic effects for populated areas within a radius of 70 km including the mexico city metropolitan area inhabited by more than 20 million people independently of the activity of the volcano lahars occur every year affecting small villages settled down flow from main ravines

regional seismic wave propagation lg and sn and pn attenuation in the arabian plate and surrounding regions an edited version of this paper was published by blackwell publishing copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02246 x http atlas geo cornell edu middleeastnorthafrica publications al damegh2004 htm

a statistical investigation of preearthquake ionospheric anomaly 1 empirical evidence of the preearthquake ionospheric anomalies peias is reported by statistically investigating the relationship between variations of the plasma frequency at the ionospheric f2 peak fof2 and 184 earthquakes with magnitude m 5 0 during 1994 1999 in the taiwan area the peia defined as the abnormal decrease more than about 25 in the ionospheric fof2 during the afternoon period 1200 1800 lt significantly occurs within 5 days before the earthquakes moreover the odds of earthquakes with peia increase with the earthquake magnitude but decrease with the distance from the epicenter to the ionosonde station these results indicate that the peia is energy related

ionospheric electron enhancement preceding the 2011 tohoku oki earthquake 1 the 2011 march 11 tohoku oki earthquake mw9 0 caused vast damages to the country large events beneath dense observation networks could bring breakthroughs to seismology and geodynamics and here i report one such finding the japanese dense network of global positioning system gps detected clear precursory positive anomaly of ionospheric total electron content tec around the focal region it started 40 minutes before the earthquake and reached nearly ten percent of the background tec it lasted until atmospheric waves arrived at the ionosphere similar preseismic tec anomalies with amplitudes dependent on magnitudes were seen in the 2010 chile earthquake mw8 8 and possibly in the 2004 sumatra andaman mw9 2 and the 1994 hokkaido toho oki mw8 3 earthquakes but not in smaller earthquakes

source radiation invariant property of local and near regional shear wave coda application to source scaling for the mw 5 9 wells nevada sequence 1 this study documents another unique property of local and regional shear wave coda that scattering in the earth s crust averages out source heterogeneities such as focal mechanism and directivity we consider two recent events which exhibited significant source directivity the first an mw 4 2 oakland hills california strike slip event on july 20 2007 resulted in uncharacteristically large amounts of damage in the montclair and south berkeley neighborhoods along strike and north west of the hypocenter but almost no damage to the south east the second event the mw 5 9 wells nevada dip slip event of february 21 2008 was well recorded by the earthscope transportable array usarray and determined to exhibit south west directivity we conclude with an example of corner frequency fc estimates from the wells sequence which showcase the coda s low variance and find that scaling is non self similar suggesting a change in dynamics between the mainshock and aftershocks

2d variations in coda amplitudes in the middle east coda amplitudes have proven to be a stable feature of seismograms allowing one to reliably measure magnitudes for moderate to large m 3 earthquakes over broad regions because smaller m 3 earthquakes are only recorded at higher frequencies for which we find larger interstation scatter amplitude and magnitude estimates for these events are more variable regional and path dependent in this article we investigate coda amplitude measurements in the middle east for 2d variations in attenuation structure one critical aspect of this effort is characterizing the propagation term to include scattering which allows us to use amplitudes out to longer distances and later in the coda we perform a tomographic inversion and find that the recovered attenuation structure is both very similar to the attenuation structure derived from direct phases and also reflective of the tectonic structure of the region we then apply the 2d attenuation corrections to several hundred events in the region and find marked improvements to our magnitude estimates as measured by interstation scattering resulting in standard deviations of less than 0 025 magnitude units at all frequencies the improvements are greatest at high frequencies which will have the largest effect on smaller magnitude events

anomalous pre seismic transmission of vhf band radio waves resulting from large earthquakes and its statistical relationship to magnitude of impending earthquakes summary to confirm the relationship between anomalous transmission of vhf band radio waves and impending earthquakes we designed a new data collection system and have documented the anomalous vhf band radio wave propagation beyond the line of sight prior to earthquakes since 2002 december in hokkaido northern japan anomalous vhf band radio waves were recorded before two large earthquakes the tokachi oki earthquake mj 8 0 mj magnitude defined by the japan meteorological agency on 2003 september 26 and the southern rumoi sub prefecture earthquake mj 6 1 on 2004 december 14 radio waves transmitted from a given fm radio station are considered to be scattered such that they could be received by an observation station beyond the line of sight a linear relationship was established between the logarithm of the total duration time of anomalous transmissions te and the magnitude m or maximum seismic intensity i of the impending earthquake for m4 m5 class earthquakes that occurred at depths of 48 54 km beneath the hidaka mountains in hokkaido in 2004 june and 2005 august similar linear relationships are also valid for earthquakes that occurred at different depths the relationship was shifted to longer te for shallower earthquakes and to shorter te for deeper ones numerous parameters seem to affect te including hypocenter depths and surface conditions of epicentral area i e sea or land this relationship is important because it means that pre seismic anomalous transmission of vhf band waves may be useful in predicting the size of an impending earthquake

the 23 500 y 14 c bp white pumice plinian eruption and associated debris avalanche and tochimilco lava flow of popocatepetl volcano mexico abstract the white pumice wp is one of the thickest and most voluminous plinian fallouts produced by popocatepetl volcano in central mexico during the late pleistocene holocene its eruption 23 500 14 c y bp 27 800 cal bp was triggered by the catastrophic failure of the sw flank of the volcano the resulting debris avalanche was highly mobile reaching 72 km from the cone with an apparent coefficient of friction l h of 0 06 the deposit covers an area of 1200 km 2 and has a volume of 10 4 km 3 this gigantic landslide characterized by exceptionally large proximal hummocks 400 m provoked the sudden decompression of the hydrothermal and magmatic systems which produced an initial blast followed by the rise of a plinian column that reached an altitude of 33 km the isopach map allows the recognition of a dispersal axis pointing toward the south where an area of 2490 km 2 was covered by 10 cm of pumice and ash the total volume of the pumice fallout was estimated at 1 9 km 3 dre dense rock equivalent pumice clasts are dacitic 62 66 wt sio 2 anhydrous basis highly vesicular 55 88 vol and display a seriate texture with phenocrysts of plagioclase hornblende augite hypersthene oxides ti magnetite and ilmenite apatite as the eruption advanced discharge rates became more intermittent and the height of the column fluctuated and finally collapsed generating pumice and ash flows that were emplaced around the volcano this short but intense activity was followed during subsequent years by rain induced lahars that reached great distances from the volcano at the same time more degassed andesitic dacitic 61 65 wt sio 2 magma was erupted effusively 4 4 km 3 dre in the new horseshoe shaped 5 km wide crater from which the tochimilco lava flow descended toward the sse where it inundated an area of 68 km 2 and reached as far as 22 km from its source since then multiple eruptions have reconstructed the summit cone almost completely obliterating the horseshoe shaped crater during the course of this catastrophic eruption vei 5 a total volume of 6 3 km 3 dre of juvenile magma pumice and lava were emitted and at least an additional 10 km 3 of pre existing rocks debris avalanche mobilized it surpasses in magnitude most other known plinian eruptions from popocatepetl and can be envisaged as an example of a worst case scenario for hazard evaluation purposes it dramatically changed the morphology of the volcano and had profound and far reaching effects beyond its immediate vicinity along rivers draining surrounding plains as well as on the lacustrine basins e g chalco to the ne a repeat of such an eruption in this densely populated area would certainly cause a major calamity of unprecedented dimensions

multisatellite observations of an intensified equatorial ionization anomaly in relation to the northern sumatra earthquake of march 2005 here we report multisatellite observations of ionospheric disturbances in relation to the occurrence of the m8 7 northern sumatra earthquake of 28 march 2005 the demeter detection of electro magnetic emissions transmitted from earthquake regions and champ challenging minisatellite payload satellite data were investigated to find possible precursory and postevent phenomena it was found that eia equatorial ionization anomaly strength expressed in the apex height derived from the champ plasma density profile was intensified along the orbits whose longitudes were close to the epicenter within about a week before and after occurrence of the earthquake increases in electron and o density along the orbits close to the epicenter were also observed in the demeter measurements the normalized equatorial plasma density derived from the demeter measurements showed intensification about a week before and after the earthquake reaching maximum the day after the shock and afterward disappearing in addition similar behavior of the eia enhancements related to the m8 0 pisco earthquake of 15 august 2007 was observed surveys of space weather and geomagnetic activities excluded the possibility that these fluctuations were caused by changes in space weather or by a geomagnetic storm statistical analyses of the longitudinal variation revealed that the eia was enhanced in the west of the epicenter and reduced in the east of the epicenter and this fits the increased conductivity model based on these observations we proposed a revised view of seismo ionospheric coupling in the region of the geomagnetic equator to explain the eia features observed in this study

a quantitative comparison between 1d and 3d source inversion methodologies application to the middle east we present a quantitative comparison between seismic moment tensor mt inversion solutions using 1d and 3d synthetic seismograms at two frequency bands for events in the middle east to assess the effects of 3d models on source studies complex geology associated with the active continental convergent margin leads to a scarcity of reliable available data necessitating a thorough examination of solution stability and robustness to assure an accurate description of sources with well characterized source parameters solutions were calculated for 195 events m w 5 5 using a full waveform mt inversion matching both phase and amplitude seismic data processed at two frequency bands compares short and long period performance for 1d and 3d synthetic seismograms an improvement in fit between data and synthetics is seen using 3d over 1d synthetic seismograms especially for complex body wave propagation and surface wave dispersion at short periods 3d synthetics provide a more robust solution compared with 1d showing a reduction in error of the source mechanism the percentage of double couple components increases with the addition of 3d structure and suggests the percentage of non double couple components is a result of poorly constrained earth structure event solutions contained in the catalog graphic 1 table s1 in the electronic supplement to this paper have an average cross correlation value of 0 87 with good amplitude ratios and are improved i e increased variance reduction yet consistent with longer period solutions from the global centroid moment tensor cmt catalog online material table of 184 event solutions from 3d moment tensor inversion 1 embed inline graphic 1 gif

neotectonic implications and regional stress field constraints on mud volcanoes in offshore southwestern taiwan abstract recently discovered numerous mud volcanoes mvs and mud diapirs mds in sw taiwan both onshore and offshore show eruption lineaments suspected to be related to neotectonic processes spatial and temporal distribution of the mvs eruption events shows an obvious switch of the lineament orientation from nne ne n s nw and e w trending in n s direction the mud volcanoes have experienced multi stage eruptions and should have occurred

popocatepetl s crater filled to the brim significance for hazard evaluation abstract after 67 years of quiescence popocatepetl volcano reawoke on december 24 1994 emitting vigorous ash plumes juvenile magma appeared for the first time on march 29 1996 with the emplacement of a dacitic lava dome inside the crater since then more than 25 dacitic domes have been extruded and destroyed by subsequent explosions on january 22 2001 the activity peaked with a strong explosion that produced pyroclastic flows that reached the timberline and ignited fires at a distance of 4 5 km from the crater these pyroclastic flows were contained within the red zone of the volcano hazards map after 10 years of discontinuous activity popocatepetl s crater is almost completely filled with lava dome rock this scenario poses a new threat to the populations settled in the orange zone intermediate hazard level because future explosions will not be contained by the crater walls and pyroclastic flows will probably reach greater distances from the crater

regional wave propagation in turkey and surrounding regions this paper was published by the american geophysical union agu copyright 2000 agu see also http www agu org journals gl gl0003 1999gl008375 pdf 1999gl008375 pdf http atlas geo cornell edu turkey publications gok et al 2000 htm

lg coda q variation across eurasia and its relation to crustal evolution an extensive set of broadband and short period seismograms from regional seismic events has been used to derive a tomographic image of broad scale variations of lg coda q for most of eurasia the image indicates that lg coda q at a frequency of 1 hz varies between about 200 and 1000 lowest q values 800 are found in four regions the east european shield the siberian shield the indian shield and the southwestern and oldest portion of the altaid belt the pattern of lg coda q variation across eurasia suggests that crustal q in any region is directly proportional to the length of time that has elapsed since the most recent episode of large scale compressional tectonic activity or upper mantle heating that occurred there we interpret the low q as resulting largely from hydrothermal fluids generated by tectonic activity or heating that now reside in cracks and permeable portions of the eurasian crust crustal q increases with time after that activity as fluids are lost to the surface or absorbed by retrograde metamorphism

lg coda q and its relation to the geology and tectonics of the middle east regional seismograms were collected to image the lateral variations of lg coda q at 1 hz q 0 and its frequency dependence in the middle east using a back projection method the data include 124 vertical component traces recorded at 10 stations during the period 1986 1996 the resulting images reveal lateral variations in both q 0 and in the turkish and iranian plateaus a highly deformed and tectonically active region q 0 ranges between about 150 and 300 with the lowest values occurring in western anatolia where extremely high heat flow has been measured the low q 0 values found in this region agree with those found in other tectonically active regions of the world throughout most of the arabian peninsula a relatively stable region q 0 varies between 350 and 450 being highest in the shield area and lowest in the eastern basins all values are considerably lower than those found in most other stable regions low q values throughout the middle east may be caused by interstitial fluids that have migrated to the crust from the upper mantle where they were probably generated by hydrothermal reactions at elevated temperatures known to occur there low q 0 values about 250 are also found in the oman folded zone a region with thick sedimentary deposits varies inversely with q 0 throughout most of the middle east with lower values 0 4 0 5 in the arabian peninsula and higher values 0 6 0 8 in iran and turkey q 0 and are both low in the oman folded zone and western anatolia

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models

2d coda and direct wave attenuation tomography in northern italy abstract a 1d coda method was proposed by mayeda et al 2003 in order to obtain stable seismic source moment rate spectra using narrowband coda envelope measurements that study took advantage of the averaging nature of coda waves to derive stable amplitude measurements taking into account all propagation site and s to coda transfer function effects recently this methodology was applied to microearthquake data sets from three subregions of northern italy i e western alps northern apennines and eastern alps because the study regions were small ranging between local to near regional distances the simple 1d path assumptions used in the coda method worked very well the lateral complexity of this region would suggest however that a 2d path correction might provide even better results if the data sets were combined especially when paths traverse larger distances and complicated regions the structural heterogeneity of northern italy makes the region ideal to test the extent to which coda variance can be reduced further by using a 2d q tomography technique the approach we use has been developed by phillips et al 2005 and is an extension of previous amplitude ratio techniques to remove source effects from the inversion the method requires some assumptions such as isotropic source radiation which is generally true for coda waves our results are compared against direct s wave inversions for 1 q and results from both share very similar attenuation features that coincide with known geologic structures we compare our results with those derived from direct waves as well as some recent results from northern california obtained by mayeda et al 2005 that tested the same tomographic methodology applied in this study to invert for 1 q we find that 2d coda path corrections for this region significantly improve upon the 1d corrections in contrast to california where only a marginal improvement was observed we attribute this difference to stronger lateral variations in q for northern italy relative to california

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

ulf geomagnetic anomalies of possible seismogenic origin observed at teoloyucan station mexico in 1999 2001 intermediate and short time analysis abstract the analysis of ulf geomagnetic field measured at teoloyucan station central mexico 11 35 735 w 19 44 45 100 n 2280 m height is presented in an intermediate 15 days and short time scale the day of the eq occurrence in relation to 7 major earthquakes occurred in mexico in 1999 2001 local changes in the fractal dynamics of the magnetic field are found to be important a pronounced fall of the fractal index is frequently observed prior to the main shock the study of the ulf resonant structure recently discovered in the frequencies fr1 10 2 11 1 mhz and fr2 13 6 14 5 mhz reveals changes in their character probably related to the processes of the earthquakes preparation the success of the observation of the mentioned anomalies specially the fractal index decrease strongly depends on how close is the station from the epicenter and what is the magnitude of the earthquake

dynamics of the ca 4965 yr 14c bp ochre pumice plinian eruption of popocatepetl volcano mexico abstract the ochre pumice op plinian fallout was produced by popocatepetl volcano in central mexico during a major plinian eruption that occurred 4965 65 14 c yr bp 3700 bc the op is part of the ochre pumice sequence ops that consists of surge fall and pyroclastic flow deposits the op plinian fallout shows a bimodal grain size distribution with poor to moderate sorting that improves progressively towards the upper beds the juvenile component is mainly pumice 83 wt whereas the accidental components consist of igneous sedimentary and metamorphic clasts from the walls of the magma chamber and or conduit the vesicularity of the pumice decreases from bottom to top of the stratigraphic sequence while the crystal and glass contents increase this suggests increasing magma degassing prior and during the eruption the chemical composition of the pumice varies insignificantly at the base it is less evolved sio 2 61 wt and it becomes slightly more silicic towards the top sio 2 63 wt pumice clasts have a crystallinity index that ranges between 10 and 25 vol and display a seriate texture with phenocrysts of euhedral plagioclase pl clinopyroxene cpx orthopyroxene opx olivine ol oxide ox apatite ap the size of the maximum lithic 2 5 cm at a horizontal distance of 19 km indicates an eruption column height of 37 41 km the isopach map allows the recognition of a dispersal axis that points towards the nne where an area of 300 km 2 was covered by 6 cm of pumice and ash a minimum volume for the op plinian fallout deposit was calculated using a minimum thickness of 6 cm found at distal outcrops and was estimated at 4 9 km 3 which corresponds to 2 km 3 of dense rock equivalent dre stratigraphic relations indicate that the entire ops was emplaced during a short time interval of a few days to weeks and consisted of three main different phases phreato magmatic plinian and vulcanian it started violently with the emplacement of surges and then culminated with the eruption of the op fallout deposit as the eruption advanced discharge rates became more intermittent and the height of the column fluctuated and finally collapsed generating pumice and ash flows that were emplaced around the volcano this short but intense activity was followed during subsequent years by the growth of domes in the crater and the emplacement of block and ash flows generated by vulcanian explosions

propagation characteristics of short period sn and lg in the middle east abstract we present propagation characteristics of the short period regional seismic phases sn and lg for the middle east digital waveform data from the iranian long period array ilpa and the global seismic network gsn stations abkt alibek turkmenistan anto ankara turkey keg kottamya egypt and kiv kislovodsk georgia were used in this study three component rotated seismograms were bandpass filtered 0 5 to 5 0 hz and examined for the presence and strength amplitude of sn and lg relative to the pn and pg phases the short period sn and lg waveforms show great variability sn propagates efficiently for paths crossing the mediterranean black and caspian seas as well as for paths passing north of the greater caucasus alborz and kopet dag mountains generally sn is not observed or propagates inefficiently for paths with segments beneath the turkish plateau and northern iranian plateau consistent with a previous study by kadinsky cade et al 1981 this study finds that the zone of inefficient sn propagation coincides with a zone of low pn velocities pn tomography lg is consistently not observed for paths crossing the mediterranean black and caspian seas lg propagates efficiently for paths crossing the northern arabian shield generally lg propagates efficiently for paths contained within the turkish iranian plateau paths in the middle east greater than about 2000 km consistently show no or little lg energy the correspondence of zones of inefficient sn propagation and low pn velocities suggests that high temperatures and partial melt lie at shallow depths in the upper mantle beneath the turkish plateau and northern iranian plateau the presence of water presumably due to subduction of hydrated oceanic crust lowers the solidus temperature and enhances partial melt lg is blocked by oceanic crustal structures as well as by structural and topographic variations associated with tectonic boundaries

statistical analysis of ulf seismomagnetic phenomena at kakioka japan during 2001 2010 to clarify and verify the ultralow frequency ulf seismomagnetic phenomena we have performed statistical studies on the geomagnetic data observed at the kakioka kak station japan during 2001 2010 we investigated the energy of ulf geomagnetic signals of the frequency around 0 01 hz using wavelet transform analysis to minimize the influences of artificial noises and global geomagnetic perturbations we used only the geomagnetic data observed at nighttime lt 2 30 a m to 4 00 a m and utilized observations from a remote station kanoya as a reference statistical results of superposed epoch analysis have indicated that ulf magnetic anomalies are more likely to appear before sizable earthquake events es 108 rather than after them especially 6 15 days before the events further statistical investigations show clearly that the ulf geomagnetic anomalies at kak station are more sensitive to larger and closer events finally we have evaluated the precursory information of ulf geomagnetic signals for local sizable earthquakes using molchan s error diagram the probability gain is around 1 6 against a poisson model the above results have indicated that the ulf seismomagnetic phenomena at kak clearly contain precursory information and have a possibility of improving the forecasting of large earthquakes

the ionospheric anomalies prior to the m9 0 tohoku oki earthquake the gps total electron content tec data were used to investigate the ionospheric abnormal behaviors prior to the 2011 tohoku oki earthquake the observations show a significant enhancement in tec on march 8 2011 and during the same period the solar activity also has a large increase both an empirical model and a theoretical model were used to check whether the tec anomalies were entirely contributed by the increase in solar radiation the comparison between the observations and the simulation results shows that only the solar radiation enhancement was not enough to produce the observed significant tec enhancement it means that some additional mechanisms such as the per earthquake ionospheric disturbance or the geomagnetic activities may play a significant role in the significant tec enhancement on march 8 the temporal spatial distribution of the extreme tec enhancement within 30 days before the earthquake was particularly pursued it is found that the extreme enhancement was persistently located in the region adjacent to the epicenter and the magnetic conjugate point for a long time of 16 h in addition a geomagnetic disturbance with kp 4 occurred on march 7 therefore the significant tec enhancement on march 8 might be related to the m9 0 tohoku oki earthquake and the geomagnetic disturbance

the ongoing dome emplacement and destruction cyclic process at popocatepetl volcano central mexico the ongoing eruptive activity of popocatepetl volcano has been characterized by emplacement and subsequent destruction of a succession of lava domes between the onset of the current eruption in 1994 and the time of this submission 38 episodes of lava dome formation and removal have been identified each dome has showed particular features related to the magma extrusion process among other manifestations dome emplacement events have been usually accompanied by relatively low intensity protracted explosions referred to as exhalations after variable times of residence emplacements have ended in partial or total destruction of the domes by strong vulcanian explosions that produced sizeable ash plumes with most of them also ejecting incandescent debris onto the volcano flanks here we present a detailed account for the observed activity related to the domes growth and destruction related seismic monitoring signals and morphological features of the domes based on 19 years of visual observations and image analysis we then discuss a model for the process of dome growth and destruction and its hazard implications

temporal and spatial precursors in ionospheric total electron content of the 16 october 1999 mw7 1 hector mine earthquake 1 in this paper temporal and spatial analyses are employed to detect seismo ionospheric precursors sips in the ionospheric total electron content tec during the 16 october 1999 mw7 1 hector mine earthquake to discriminate anomalies caused by global effects such as solar radiations magnetic storms etc and local effects such as earthquake we cross examine the gps tecs and their gradients in the eastward and northward directions at epicenter centers of the hector mine area and the other two reference areas at similar magnetic latitudes in europe and japan temporal variations of the northward tec gradient suggest sips most likely appearing on days 6 5 before the earthquake a global search by using the tec of the global ionosphere map shows that the tec increase and decrease anomalies continuously and specifically appear around the epicenter on day 5 before the earthquake

observations and simulations of seismoionospheric gps total electron content anomalies before the 12 january 2010 m7 haiti earthquake 1 in this paper the total electron content tec of the global ionosphere map gim is used to detect seismoionospheric anomalies associated with the 12 january 2010 m7 haiti earthquake and an ionospheric model is applied to simulate the detected anomalies the gim temporal variation shows that the tec over the epicenter significantly enhances on 11 january 2010 1 day before the earthquake the latitude time tec ltt plots reveal three anomalies 1 the northern crest of equatorial ionization anomaly eia moves poleward 2 the tecs at the epicenter and its conjugate increase and 3 the tecs at two dense bands in the midlatitude ionosphere of 35 n and 60 s further enhance the spatial analysis demonstrates that the tec enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area the simulation well reproduces the three gim tec anomalies which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period

sedimentary basins and the blockage of lg wave propagation in the continents the phenomenon of lg blockage where lg is strongly attenuated by crustal heterogeneities poses a serious problem to ctbt monitoring because lg is an important seismic phase for discrimination this paper examines blockage in three continental regions where the lg blockages may be caused by large enclosed sedimentary basins along the propagation path the barents sea basin blocks lg propagation across the barents sea from the russian nuclear test sites at novaya zemlya to scandinavian stations also early lg waves are observed in sn codas on norsar noress and arcess recordings of novaya zemlya explosions where direct lg is blocked early lg waves may have resulted from sn to lg mode conversion at the contact between the barents basin and the kola peninsula the northern and southern caspian sea basins also block lg waves from pnes and earthquakes perhaps due to thick low velocity low q sediments replacing the granitic layer rocks in the crust lg blockage has also been observed in the western mediterranean levantine basin due to low q sediments and crustal thinning a basin capture model is proposed to explain lg blockage in sedimentary basins in this model shear waves that reverberate in the crust and constitute the lg wave train are captured delayed and attenuated by thick low velocity sediments that replace the granitic layer rocks of the upper crust along part of the propagation path sn waves which propagate below the basin would not be blocked and in fact the blocked lg waves may be diverted downward into sn waves by the low velocity sediments in the basin

observations of the quasi 2 day wave from the high resolution doppler imager on uars a strong westward traveling oscillation with a period of 2 days and zonal wave number 3 is observed in the mesospheric and lower thermospheric winds from the high resolution doppler imager on the upper atmosphere research satellite the important events happen in january july and september october of which the occurrence in january is the strongest with an amplitude over 60ms 1 detailed analyses for the periods of january 1992 and january 1993 reveal a cause and effect relationship in the wave developing process at 95km the global structures of the wave amplitude and phase are also presented

precursory effects in the subionospheric vlf signals for the kobe earthquake abstract the subionospheric vlf omega signal transmitted from tsushima japan geographic coordinates 34 37 n 129 27 e was continuously received at inubo 35 42 n 140 52 e this data was analyzed during an 8 month period centered on the great hyogo ken nambu kobe earthquake m g 7 2 on 17 january 1995 the epicenter located inside of fresnel zone of the vlf path to clarify the possible effect we developed the special tt terminator time method of data processing which was useful for our short vlf path distance 1000 km we discovered a statistically significant change of tt characteristics which began a few days before the main shock and probably continued a few weeks after it as a transient oscillation with period 10 days by simple modelling it was shown that tt changes could be caused by the decrease of the vlf reflection height by 2 km the possible underlying mechanisms of the effect are not defined however an increase of the regular electric field due to radon exhalation before the earthquake or an intensification of planetary waves by seismically influenced atmospheric turbulence might be considered

an application of the coda methodology for moment rate spectra using broadband stations in turkey a recently developed coda magnitude methodology was applied to selected broadband stations in turkey for the purpose of testing the coda method in a large laterally complex region as found in other albeit smaller regions coda envelope amplitude measurements are significantly less variable than distance corrected direct wave measurements i e l sub g and surface waves by roughly a factor 3 to 4 despite strong lateral crustal heterogeneity in turkey they found that the region could be adequately modeled assuming a simple 1 d radially symmetric path correction after calibrating the stations isp iskb and malt for local and regional distances single station moment magnitude estimates m sub w derived from the coda spectra were in excellent agreement with those determined from multistation waveform modeling inversions exhibiting a data standard deviation of 0 17 though the calibration was validated using large events the results of the calibration will extend m sub w estimates to significantly smaller events which could not otherwise be waveform modeled the successful application of the method is remarkable considering the significant lateral complexity in turkey and the simple assumptions used in the coda method

trenchward plio quaternary volcanism migration in the trans mexican volcanic belt the case of the sierra nevada range the miocene quaternary trans mexican volcanic arc is thought to have grown southwards i e trenchward since the pliocene this theory is mainly supported by roughly n s directed polygenetic volcanic ranges along which volcanic activity migrates southwards with time we investigated the eruptive history of one of these ranges the sierra nevada east boundary of mexico city basin by compiling literature ages and providing new k ar dates our k ar ages are the first ones for the northernmost tlaloc and telapon volcanoes and for the ancestral popocatepetl nexpayantla the obtained ages reveal that the four stratovolcanoes forming the range worked contemporaneously during most of the middle to late pleistocene however taking into account the onset of the volcanic activity a southward migration is evidenced along the sierra nevada volcanism initiated at its northern tip at least 1 8 ma ago at tlaloc volcano extended southwards 1 ma ago with iztaccihuatl and appeared at its southern end 329 ka ago with the nexpayantla cone such a migration would be most probably primarily driven by cocos slab roll back and steepening rather than by regional crustal tectonics which played a secondary role by controlling the apparent alignment of the volcanoes

time resolved study of charge generation and propagation in igneous rocks electrical resistivity changes ground potentials electromagnetic em and luminous signals preceding or accompanying earthquakes have been reported many times in addition to ground uplift and tilt and other parameters however no concept exists that would tie these diverse phenomena together into a physically coherent model using low to medium velocity impacts to measure electrical signals with microsecond time resolution it is observed that when gabbro and diorite cores are impacted at relatively low velocities 100 m s highly mobile charge carriers are generated in a small volume near the impact point they spread through the rocks causing electric potentials exceeding 400 mv em and light emission as the charge cloud spreads the rock becomes momentarily conductive when a granite block is impacted at higher velocity 1 5 km s the propagation of the p and s waves is registered through the transient piezoelectric response of quartz after the sound waves have passed the surface of the granite block becomes positively charged suggesting the same charge carriers as observed during the low velocity impact experiments expanding from within the bulk during the next 2 3 ms the surface potential oscillates indicating pulses of electrons injected from ground and contact electrodes the observations are consistent with positive holes e g defect electrons in the o2 sublattice traveling via the o 2p dominated valence band of the silicate minerals the positive holes propagate as charge clouds rather than as classical em waves before activation they lay dormant in form of electrically inactive positive hole pairs php chemically equivalent to peroxy links o3x oo xo3 with x si4 al3 etc phps are introduced into the minerals by way of hydroxyl o3x oh which all nominally anhydrous minerals incorporate when crystallizing in h2o laden environments the fact that positive holes can be activated by low energy impacts and their attendant sound waves suggests that they can also be activated in the crust by microfractures during the dilatancy phase depending on where in the stressed rock volume the charge carriers are activated they will form rapidly moving or fluctuating charge clouds that can account for earthquake related electrical signals and em emission wherever such charge clouds intersect the surface high fields are expected causing electric discharges and earthquake lights

variations of ionospheric total electron content during the chi chi earthquake on 20 september1999 ut 21 septemberin local time lt a large earthquake mw 7 7 struck central taiwan nearthe small town of chi chi the greatest plasma frequency in the ionosphere fof2 observed by the chung li ionosonde 25 0 n 121 2 e reveals three clear precur sors at 1 3 and 4 days prior to the earthquake this paper examines the ionospheric total electron content tec ob served by a network of the global positioning system gps receivers in taiwan area it is found that variations in fof2 and overhead tec recorded at chung li have a similar ten dency combining the data of the network of 13 gps re ceivers time and spatial variations of tec prior to the chi chi earthquake are examined results show that the equa torial anomaly crest moves equatorward and its tec value significantly decreases 1 3 and 4 days before the earth quake a comparison between the disturbed and reference previous 15 day median days confirms that tec decreases significantly around the epicenter in the afternoons of these days finally possible mechanisms are proposed and dis cussed

elf vlf recordings during the 11 march 2011 japanese tohoku earthquake 1 broadband elf vlf radio recordings 0 2 40 khz were made at a site in onagawa japan located 102 km from the epicenter of the m9 0 11 march 2011 earthquake the fifth most powerful earthquake in recorded history the receiver operated for about two minutes after the start of the earthquake after which the receiver lost power examination of the vlf data shows no radio emissions preceding or coincident with the onset of the earthquake however once the secondary seismic waves reached the receiver a number of impulses and diffuse noise bands arose which may result from the entire power grid shaking or from radio emissions from compressing rocks examination of the elf data 0 2 1 khz show no precursor effect in the hours preceding the earthquake examination of vlf data from narrowband transmitters shows no anomalous activity in the days or weeks preceding the earthquake our instrument low frequency cut off is 200 hz and thus we cannot comment on emissions in the ulf range 10 hz

electro magnetic earthquake bursts and critical rupture of peroxy bond networks in rocks abstract we propose a mechanism for the low frequency electromagnetic emissions and other electromagnetic and electric phenomena which have been associated with earthquakes the mechanism combines the critical earthquake concept and the concept of crust acting as a charging electric battery under increasing stress the electric charges are released by activation of dormant charge carriers in the oxygen anion sublattice called peroxy bonds or positive hole pairs php where a php represents an o 3 x oo yo 3 with x y si 4 al 3 i e o in a matrix of o 2 of silicates we propose that php are activated by plastic deformations during the slow cooperative build up of stress and the increasingly correlated damage culminating in a large critical earthquake recent laboratory experiments indeed show that stressed rocks form electric batteries which can release their charge when a conducting path closes the equivalent electric circuit we conjecture that the intermittent and erratic occurrences of em signals are a consequence of the progressive build up of the battery charges in the earth crust and of their release when crack networks percolate through the stressed rock volumes providing a conductive pathway for the battery currents to discharge em signals are thus expected close to the rupture either slightly before or after that is when percolation is most favored the proposed mechanism should be relevant for the broader understanding of fractoemissions

tomographic imaging of lg and sn propagation in the middle east observations based on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation lg and sn is very complex in the middle east accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations we have compiled a large data set of regional and local seismograms recorded in the middle east this data set comprises approximately four years of data from national short period networks in turkey and syria data from temporary broadband arrays in saudi arabia and the caspian sea region and data from gsn mednet and geofon stations in the middle east we have used this data set to decipher the character and pattern of regional seismic wave propagation we have mapped zones of blockage as well as inefficient and efficient propagation for lg pg and sn throughout the middle east two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the middle east we observe evidence of major increase in lg attenuation relative to pg across the bitlis suture and the zagros fold and thrust belt corresponding to the boundary between the arabian and eurasian plates we also observe a zone of inefficient sn propagation along the dead sea fault system which coincides with low pn velocities along most of the dead sea fault system and with previous observations of poor sn propagation in western jordan our observations indicate that in the northern portion of the arabian plate south of the bitlis suture there is also a zone of inefficient sn propagation that would not have been predicted from prior measurements of relatively low pn velocities mapped high attenuation of sn correlates well with regions of cenozoic and holocene basaltic volcanism these regions of uppermost mantle shear wave attenuation most probably have anomously hot and possibly thin lithosphere

atmospheric anomalies observed during earthquake occurrences 1 appearance of anomalies in the atmosphere before earthquakes eqs has been verified through observation of anomalous transmission of vhf electromagnetic em waves beyond line of sight anomalous increase of the received intensity for a few minutes several hours on a day was identified by the previous 15 day running median and its inter quartile range the cross correlation between the eq occurrences and the anomalies shows that the appearance of anomalies was significantly enhanced within 5 days before m 4 8 eqs the one day average number of the anomaly appearance within 5 days was found 2 4 times larger than that of other days through the polarization measurement of the received em waves the anomalies were found to occur in the atmosphere index terms 6904 radio science atmospheric propagation 6964 radio science radio wave propagation 7223 seismology seismic hazard assessment and prediction citation fujiwara h m kamogawa m ikeda j y liu h sakata y i chen h ofuruton s muramatsu y j chuo and y h ohtsuki 2004 atmospheric anomalies observed during earthquake occurrences geophys res lett 31 l17110

sn attenuation in the anatolian and iranian plateau and surrounding regions an edited version of this paper was published in geophysical research letters by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018020 shtml http atlas geo cornell edu turkey publications gok et al 2003 htm

ionosphere plasma bubbles and density variations induced by pre earthquake rock currents and associated surface charges 1 recent ionospheric observations indicate that the total electron content tec may anomalously decrease or increase up to 5 20 before the occurrence of big earthquakes the ionospheric density variations can be caused by earth surface charges currents produced from electric currents associated with the stressed rock we formulate a coupling model for the stressed rock earth surface charges atmosphere ionosphere system the stressed rock acts as the dynamo to provide the currents for the coupling system the electric fields and currents in the atmosphere and the lower boundary of ionosphere are obtained by solving the current continuity equation j 0 where j is the current density a three dimensional ionosphere simulation code is then used to study the ionospheric dynamics based on the obtained electric fields and currents the simulation results show that a current density jrock 0 2 10 a m2 in an earthquake fault zone is required to cause daytime tec variations of 2 25 the simulation results also show that a current density jrock 0 01 1 a m2 can lead to nighttime tec variations of 1 30 as well as the formation of a nighttime plasma bubble equatorial spread f extending over the whole magnetic flux tube containing the earthquake epicenter we suggest that observations of daytime and nighttime tec variations and a nighttime plasma bubble within the affected region can be used as precursors for earthquake prediction

a statistical study on the correlation between lower ionospheric perturbations as seen by subionospheric vlf lf propagation and earthquakes 1 the subionospheric vlf lf propagation is extensively used to investigate the lower ionospheric perturbation in possible association with earthquakes an extensive period of data over 7 yr from january 2001 to december 2007 and a combination of different propagation paths in and around japan are used to examine the statistical correlation between the vlf lf propagation anomaly average nighttime amplitude dispersion and nighttime fluctuation and earthquakes with magnitude 6 0 it is then found that the propagation anomaly exceeding the 2 standard deviation criterion indicating the presence of ionospheric perturbation is significantly correlated with earthquakes with shallow depth 40 km finally the mechanism of seismoionospheric perturbations is discussed

source and behavior of pyroclastic density currents generated by vulcanian style explosions of popocatepetl volcano mexico on 22 january 2001 abstract since 1994 popocatepetl volcano has extruded 85 lava domes each of which has been destroyed by vulcanian style explosions the paroxysmal vulcanian explosion of 22 january 2001 has been unique by generating multiple pyroclastic density currents pdcs scientists and civil protection authorities have used those pdcs to remap the high risk hazard zone of the volcano although little study has been carried out to understand the generation and evolution of those pdcs here we examine 38 stratigraphic sections and analyze the granulometry componentry vesicularity and petrology glass melt inclusions in plagioclase of collected samples to interpret the origins of the vulcanian explosions and the pdc behavior the 22 january event generated two series of dense pdcs that detached from the base of the eruption column the first set of pdcs traveled northwest across a glacier on the volcano partially scouring and melting the ice that hours later generated a lahar two pulses of these pdcs were confined within a large ravine surpassed the slope break and traveled up to 3 km away from the vent the deposits are matrix supported throughout their extent the second set of pdcs traveled to the northeast mainly as unconfined currents that split into two lobes prior to the slope break the farthest traveled current followed a western ravine and reached the forest 3 5 km from the summit the eastern lobe buried a local hiking hut and reached 2 1 km the deposits from these northeastern currents are massive and block supported all deposits volume of 5 71 105 m3 have finger like morphology with levees and frontal snouts all pdcs flowed as a dense basal granular current with turbulent upper clouds at minimum speeds of 7 10 m s in terms of hazards pdcs that interact with glaciers on the volcano are expected to travel farther and potentially generate extensive lahars at present small intermittent patches of glacier occur on the northern upper slopes of the volcano the components of the deposits are in order of abundance black scoria 53 62 wt sio2 banded scoria pumice 63 wt sio2 dome lithics 60 61 wt sio2 accidental lithics and free crystals juvenile pumice and scoria contain phenocrysts of plagioclase an47 10 clinopyroxene en48 3 orthopyroxene en64 1 ilmenite and titanomagnetite set in a rhyolitic glass pumice clast 74 39 wt sio2 or microlite rich matrix scoria clast the dome lithics also contain these phenocrysts as well as rare olivine phenocrysts fe2 fe2 mg 0 1 dissolved h2o co2 contents in melt inclusions hosted by pumice plagioclase phenocrysts suggest the felsic magma was stored at depths of 2 4 km thus the 2001 event was triggered by the injection of mafic magmas into a small volume of felsic magma probably forming dikes left from the previous eruptive episode we propose that the vulcanian explosions tap a column of magma 2 km depth equivalent to the volume that contained the felsic dikes this mechanism has been acting during the destruction of all summit domes of the ongoing eruption of the volcano

estimating absolute site effects the authors use previously determined direct wave attenuation functions as well as stable coda derived source excitation spectra to isolate the absolute s wave site effect for the horizontal and vertical components of weak ground motion they used selected stations in the seismic network of the eastern alps and find the following 1 all hard rock sites exhibited deamplification phenomena due to absorption at frequencies ranging between 0 5 and 12 hz the available bandwidth on both the horizontal and vertical components 2 hard rock site transfer functions showed large variability at high frequency 3 vertical motion site transfer functions show strong frequency dependence and 4 h v spectral ratios do not reproduce the characteristics of the true horizontal site transfer functions 5 traditional relative site terms obtained by using reference rock sites can be misleading in inferring the behaviors of true site transfer functions since most rock sites have non flat responses due to shallow heterogeneities resulting from varying degrees of weathering they also use their stable source spectra to estimate total radiated seismic energy and compare against previous results they find that the earthquakes in this region exhibit non constant dynamic stress drop scaling which gives further support for a fundamental difference in rupture dynamics between small and large earthquakes to correct the vertical and horizontal s wave spectra for attenuation they used detailed regional attenuation functions derived by malagnini et al 2002 who determined frequency dependent geometrical spreading and q for the region these corrections account for the gross path effects i e all distance dependent effects although the source and site effects are still present in the distance corrected spectra the main goal of this study is to isolate the absolute site effect as a function of frequency by removing the source spectrum moment rate spectrum from the distance corrected s wave spectra typically removing the s wave source spectrum is difficult because of inadequate corrections for the source radiation pattern directivity and random interference in addition to complexities near the source 2 d and 3 d structure beneath the recording site will result in an azimuth dependent site effect since the direct wave only samples a narrow range in take off and back azimuth angles multi station averaging is needed to minimize the inherent scatter to minimize these complicating effects they apply the coda methodology outlined by mayeda et al 2003 to obtain stable moment rate spectra this methodology provides source amplitude and derived source spectra that are a factor of 3 to 4 times more stable than those derived from direct waves since the coda is commonly thought of as scattered energy that samples all ray parameters and back azimuths it is not very sensitive to the source radiation pattern and 3 d structure this property makes it an excellent choice for use in obtaining average properties of the source site and path effects in a region due to the characteristics of the techniques used in this study all the inverted quantities are azimuthally averaged since the aximuthal information is lost in the processing

subionospheric vlf signal perturbations possibly related to earthquakes a likely vlf subionospheric signal effect related to seismic activity was first reported by hayakawa et al 1996a b in association with the great kobe earthquake we have analyzed similar data during periods around 10 other great earthquakes magnitude m 6 in order to understand the main features of such an effect the following characteristics emerged from our analysis the effect appears as a transient oscillation with a 5 to 10 day period which is initiated a few days before a large earthquake and decays over a few days to weeks after it it is mainly related to crustal earthquakes it appears when resonant atmospheric oscillations with periods in a range of 5 11 days exist before the earthquake the seismic influence on the vlf signal is probably explained by the generation of long period gravity waves during the earthquake process and their intensification at heights of 70 90 km

results of ultra low frequency magnetic field measurements during the guam earthquake of 8 august 1993 we report the results of measurements of ultra low frequency magnetic noise during a large earthquake ms 7 1 at guam of 8 august 1993 depth 60 km the ulf observing system is located in the guam island about 65 km from the epicenter several distinct features of this analysis are summarized 1 we have proposed rather sophisticated statistical analyses monthly mean standard deviation in order to estimate the wave intensity and polarization i e ratio z h 2 a comparison between the ulf wave activity and kp is useful in distinguishing between the space geomagnetic pulsations and non space emissions 3 then the use of the ratio z h is found to be of essential importance in discrimating the emissions presumably of seismic origin from space plasma waves 4 the statistical analysis of the temporal evolution of this ratio has yielded that it shows a broad maximum only about one month before the earthquake and this suggests that the emissions during this period are very likely to be magnetic precursors 5 the temporal variation of z component is similar to that for the loma prieta earthquake such that it shows a broad maximum ten days two weeks before the earthquake and another increase a few days before the earthquake 6 the emissions presumably associated with the earthquake are of noise like nature and their main frequency is 0 02 0 05 hz with maximum intensity 0 1 nt

a systematic compilation of earthquake precursors article a survey of published scientific literature was undertaken to identify and catalog observed earthquake pre cursors the earthquake precursors selected for analysis included electric and magnetic fields gas emissions groundwater level changes temperature changes surface deformations and seismicity for each of these precursors the published scientific literature was searched to document the statistics of each reported earth quake precursor spatial extent time duration amplitude signal noise ratio to analyze dependence of the observable for each precursor on earthquake magnitude and to explore proposed physical models to explain eachearthquakeprecursor somegeneralcharacteristics wereobservedfortheseprecursoryphenomena first the largest amplitude precursory anomalies tend to occur before the largest magnitude earthquakes also the number of precursory anomalies tends to increase the closer in time to the occurrence of the earthquake finally theprecursoryanomaliestendtooccurclosetotheeventualepicenterof theearthquake ingeneral the physical models indicate that all of the precursory phenomena are related to deformation that occurs near the fault prior to the main earthquake while the models provide plausible physical explanations for the pre cursors there are many free parameters in the models that are poorly resolved

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

investigating seismoionospheric effects on a long subionospheric path we examine the possibility of earthquake precursors influencing the subionospheric propagation of vlf transmissions we consider the long 12 mm path from northeastern united states to faraday antarctica 65 s 64 w during 1990 1995 and investigate the subionospheric amplitude variation of signals from the naa communication transmitter 24 0 khz 1 mw in cutler maine with particular emphasis on possible changes induced by seismic events occurring in south america we have analyzed the changes in timing of modal minima generated by the passage of the sunrise terminator over the andes i e the vlf terminator time tt method the anomalous variations in timing throughout the year are of a size and occurrence frequency similar to those previously reported i e 0 5 1 hour and 1 2 per month however we find that in these anomalous cases the time of the sunrise modal minimum does not change significantly but rather the minimum becomes insufficiently deep to be detected and the time of the next nearest minimum is logged our analysis indicates that the occurrence rate of successful earthquake predictions using the tt method cannot be distinguished from that of chance additionally the level of false earthquake prediction using the tt method is high

results of ulf magnetic field measurements near the epicenters of the spitak ms 6 9 and loma prieta ms 7 1 earthquakes comparative analysis the characteristics of the ulf magnetic field emissions measured at two magnetic observatories in the republic of georgia prior to and after the ms 6 9 earthquake that occurred near spitak armenia on december 7 1988 are compared with the apparently similar emissions associated with the ms 7 1 earthquake that occurred near loma prieta california on october 17 1989 the main features of the spitak measurements according to observations made at the dusheti station 128 km to the spitak epicenter as compared with the loma prieta measurements which were made at corralitos california 7 km to the loma prieta epicenter are the following 1 the intensity of ulf background activity started growing 3 to 5 days before the spitak earthquake whereas the corresponding increase in activity began 12 days before the loma prieta earthquake 2 a substantial ulf emission burst was recorded at dusheti starting 4 hours prior to the main shock a similar large burst of ulf activity commenced 3 hours before the loma prieta event and continued until the occurrence of the main shock 3 ulf activity remained high for about two weeks after the spitak earthquake and for several months after the loma prieta earthquake 4 ulf noise bursts were observed 1 to 6 hours before powerful aftershocks at spitak during the period of enhanced activity but there was no conclusive link between the ulf noise at corralitos and the after shocks a major difference in the ulf activity preceding the two earthquakes is a difference in amplitude 0 2 nt at spitak and 5 nt at loma prieta but this is easily explained as being caused by the different distances of the observation stations from the epicenters

gradual reduction in ionospheric f 2 region before the 2013 lushan earthquake contributed to the forthcoming earthquake or solar activity ionospheric anomalies before earthquakes during geomagnetic quiet conditions have been extensively discussed due to the importance of earthquake prediction however because of the high variability of ionosphere a real caution should be adopted before attributing the observations to seismo ionospheric precursors sips in an investigation of contradictory results in ionospheric variation before 2013 lushan earthquake we examine the ionospheric variation versus solar activity in order to assess the influence of solar activity of 27 day periodicity on ionospheric variation a quadratic regression model is developed by using the data of f2 layer critical frequency fof2 in april of 2008 2014 using the model ionospheric variation before the 2013 lushan earthquake is analyzed the results show that fof2 was strongly correlated with solar activity index f10 7 and had a low correlation with the remaining by eliminating the contribution of solar radiation which indicates that the gradual reduction in fof2 before the earthquake was contributed to the variation of solar radiation rather than the forthcoming earthquake

observations of the 5 day wave in the mesosphere and lower thermosphere the 5 day planetary wave has been detected in the winds measured by the high resolution doppler imager hrdi on the upper atmosphere research satellite uars in the mesosphere and lower thermosphere 50 110 kin the appearances of the 5 day wave are transient with a lifetime of 10 20 days in the two year data set the structures of selected 5 day wave events are in generally good agreement with the 1 1 rossby normal mode for both zonal and meridional components a climatology of the 5 day wave is presented for an altitude of 95 km and latitudes mainly between 40os and 40on

moment magnitudes of local regional events from 1d coda calibrations in the broader middle east region abstract reliable moment magnitude estimates for seismic events in the middle east region can be difficult to obtain due to the uneven distribution of stations the complex tectonic structure and regions of high attenuation in this study we take advantage of the many new broadband seismic stations that have become available through improved national networks and numerous temporary deployments we make coda envelope amplitude measurements for 2247 events recorded by 68 stations over 13 narrow frequency bands ranging between 0 03 and 8 hz the absolute scaling of these spectra was calculated based on independent waveform modeling solutions of the moment magnitudes for a subset of these events to avoid circularity using our 1d path calibrations we determined coda based magnitudes for a majority of the events we obtain fairly good agreement with waveform modeled seismic moments for the larger events m w 4 5 at low frequencies 0 7 hz because of unaccounted 2d path effects as well as mixing of both sn coda and lg coda which have different attenuation behavior this scatter leads to increased variance in the magnitudes estimated for smaller events in which low frequency amplitudes are below the noise levels and the higher frequencies are the only signals available we quantify the expected variance in coda envelope amplitudes as a function of frequency using interstation scatter as our metric the net results of this study provide thousands of new 1d coda magnitude estimates for events in the broad region as well as the necessary initial starting model for use in a new related 2d coda study pasyanos et al 2016 online material table of site terms and moment magnitudes

seismo ionospheric signatures prior to m 6 0 taiwan earthquakes this paper examines variations of the greatest plasma frequency in the ionosphere fof2 recorded by the chung li ionosonde 25 0 n 121 1 e before m 6 0 earthquakes during 1994 1999 the 15 day running median and the associated inter quartile range are utilized as the reference and the upper or lower bounds to monitor the ionospheric fof2 variations for finding seismo ionospheric signatures precursors of the earthquakes it is found that precursors in the form of the recorded fof2 falling below its associated lower bound around 1200 1700 lt appear 1 6 days prior to these earthquakes on september 20 1999 ut september 21 taiwan local time a large mw 7 7 earthquake struck central taiwan near the small town of chi chi we analyzed the fof2 and found three clear precursors 1 3 and 4 days prior to the chi chi earthquake

short term earthquake prediction current status of seismo electromagnetics abstract loss of human lives as a result of earthquakes is caused overwhelmingly by the collapse of buildings within less than a few minutes of main shocks the most urgent countermeasure consists of two key elements one is strengthening of weak structures and the other is short term earthquake prediction short term prediction needs precursors although some promising precursors are reported the prevailing views in japan and elsewhere are overly pessimistic the pessimism largely roots in the fact that short term precursors are generally non seismic and tools developed for seismology are not designed to detect them nonetheless nationally funded large scale earthquake prediction programs always emphasize the need to reinforce seismometer networks they do not take into account the views of those in the science community who point to the importance of non seismic precursors while there are well founded causes to be skeptical the situation needs to be improved one reason for skepticism is that the observations of precursors have not yet been perfect enough and another is that some important fundamental aspects of non seismic precursors are still unresolved we review some of these problems

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

gas composition of popocatepetl volcano between 2007 and 2008 ftir spectroscopic measurements of an explosive event and during quiescent degassing abstract on december 1 2007 the solar absorption infrared spectra of the popocatepetl volcanic plume was recorded during an eruptive event and complementarily on november 17 2008 the passive quiescent degassing was measured from the same site a portable ftir spectrometer with a scanning mirror for fast tracking of the sun provided the flexibility quality and simplicity needed for field deployment slant columns of the gases so 2 hcl hf and sif 4 were retrieved and strong differences could be observed when comparing gas ratios in both time periods during the explosive eruption the so 2 hcl ratio was three times greater and the hf hcl ratio was slightly smaller than during passive degassing while the ratios among so 2 hcl hf and sif 4 describe the chemical composition of the volcanic gas mixture the sif 4 hf ratio provides information about the equilibrium temperatures of the stored gases which in this study were calculated at 150 and 185 c for the explosive and quiescent degassing episodes respectively we conclude that cooling of lava domes in the crater precedes vulcanian explosions as suggested by schaaf et al 2005 based on so 2 flux grutter et al 2008 and measurements and data from the november 2008 event the average fluxes for hcl hf sif 4 and f through quiescent degassing are estimated to be 204 22 7 9 8 and 31 7 tons day respectively these values are similar to those reported by love et al 1998 more than 10 yrs ago

the 25 april 2015 nepal earthquake investigation of precursor in vlf subionospheric signal we present a critical analysis of the observations and interpretation of vlf sub ionospheric measurements related to the main nepal gorkha earthquake which occurred on april 25 2015 mw7 8 and its major aftershock on may 12 2015 mw7 3 the vlf narrowband signal used is from nwc 19 8 khz vlf transmitter located in australia and recorded at allahabad lat 25 41 n long 81 93 e allahabad is located very close 360 km to these earthquake eq epicenters two widely used analysis viz 1 terminator time and 2 night time fluctuation techniques are applied to extract seismic related effects in the nwc narrowband vlf data the terminator time analysis yields statistically significant shifts of 45 and 26 minutes respectively in evening terminator time in the nwc vlf amplitude signal one day before both the earthquakes the nighttime fluctuation method shows a consistent statistically significant increase in three parameters one day before the earthquake the observed terminator time and nighttime fluctuation shifts were associated with these earthquakes only after scrutinizing possible contributions from other potential sources such as solar activity other earthquakes on the signal path meteorological disturbances such as lightning activity wind speed temperature etc along the transmitter receiver great circle path the vlf sub ionospheric signal analysis results unambiguously point towards the presence of seismically excited atmospheric gravity waves agws during these major earthquakes and their important role in providing the coupling between the seismic source region and overlying ionosphere

crustal structure below popocatepetl volcano mexico from analysis of rayleigh waves an array of ten broadband stations was installed on the popocatepetl volcano mexico for five months between october 2002 and february 2003 26 regional and teleseismic earthquakes were selected and filtered in the frequency time domain to extract the fundamental mode of the rayleigh wave the average dispersion curve was obtained in two steps firstly phase velocities were measured in the period range 2 50 s from the phase difference between pairs of stations using wiener filtering secondly the average dispersion curve was calculated by combining observations from all events in order to reduce diffraction effects the inversion of the mean phase velocity yielded a crustal model for the volcano which is consistent with previous models of the mexican volcanic belt the overall crustal structure beneath popocatepetl is therefore not different from the surrounding area and the velocities in the lower crust are confirmed to be relatively low lateral variations of the structure were also investigated by dividing the network into four parts and by applying the same procedure to each sub array no well defined anomalies appeared for the two sub arrays for which it was possible to measure a dispersion curve however dispersion curves associated with individual events reveal important diffraction for 6 s to 12 s periods which could correspond to strong lateral variations at 5 to 10 km depth

electric and magnetic phenomena observed before the volcano seismic activity in 2000 in the izu island region japan significant anomalous changes in the ultra low frequency range 0 01 hz were observed in both geoelectric and geomagnetic fields before the major volcano seismic activity in the izu island region japan the spectral intensity of the geoelectric potential difference between some electrodes on niijima island and the third principal component of geomagnetic field variations at an array network in izu peninsula started to increase from a few months before the onset of the volcano seismic activity culminating immediately before nearby magnitude 6 class earthquakes appearance of similar changes in two different measurements conducted at two far apart sites seems to provide information supporting the reality of preseismic electromagnetic signals

coda derived source parameters of earthquakes and their scaling relationships in the korean peninsula we applied the coda derived source spectrum method of mayeda et al 2003 to earthquakes in and around the korean peninsula after empirical calibra tions we derived source spectra of the earthquakes from the coda derived spectra we estimated valuable source parameters such as the seismic moment corner frequency and radiated energy for small events with mw 3 5 we derived simple linear relation ships between the coda spectral amplitudes and local magnitudes reported from the korea meteorological administration and korea institute of geoscience and mineral resources these relationships can be used to estimate stable local magnitudes for future earthquakes using a small number of stations to investigate whether the earth quakes occurring in this region obey self similarity we examined the scaling relation ships between dynamic and static source parameters such as the corner frequency radiated energy and scaled energy versus seismic moment the scaling relationship between the corner frequency and seismic moment showed clear nonself similarity with a scaling parameter of 0 54 this value is more or less consistent with previous results for different regions scaling relations of radiated energy and scaled energy versus the seismic moment also show size dependent behavior that cannot be explained by self similarity this result implies that the rupture dynamics of small and large earthquakes are different in this region our observation provides further evidence supporting the nonself similarity of earthquakes

investigation of ionospheric electron content variations before earthquakes in southern california 2003 2004 1 it has been proposed that earthquakes are preceded by electromagnetic signals detectable from ground and space based measurements ionospheric anomalies such as variations in the electron density a few days before earthquakes are one of the precursory signals proposed since global positioning system gps data can be used to measure the ionospheric total electron content tec the technique has received attention as a potential tool to detect ionospheric perturbations related to earthquakes here we analyze 2 years 2003 2004 of data from the southern california integrated gps network scign a dense network of 265 continuous gps stations centered on the los angeles basin for possible precursors this time period encompasses the december 2003 m6 6 san simeon and september 2004 m6 0 parkfield earthquakes we produce tec time series at all scign sites and apply three different statistical tests to detect anomalous tec signals preceding earthquakes we find anomalous tec signals but no statistically significant correlation in time or in space between these tec anomalies and the occurrence of earthquakes in southern california for the 2003 2004 period this result does not disprove the possibility of precursory phenomena but show the signal to noise ratio of a hypothetical tec precursor signature is too low to be detected by the analysis techniques employed here precursors may still be revealed for future large earthquakes in well instrumented areas such as california and japan if the tests can be developed into techniques that can better separate external influences from the actual tec signal

suspected seismo ionospheric coupling observed by satellite measurements and gps tec related to the m7 9 wenchuan earthquake of 12 may 2008 anomalous changes in the ionospheric conditions related to the wenchuan earthquake of 12 may 2008 are investigated using electron density ne from detection of electro magnetic emissions transmitted from earthquake regions demeter and champ satellites electric field from demeter and gps total electron content tec maps the normalized ne from the demeter satellite reveal that the previously reported tec increments before the earthquake can be considered as fragments of the gradual equatorial ionization anomaly eia enhancements near the epicenter longitude that began approximately 1 month before the earthquake and reached its maximum with an exceptionally large strength index 8 days prior to the main shock this feature is indirectly confirmed through the champ ne and gps tec data following the eia intensity peak disturbances in the ne and o density were observed in the nightside based on the concurrent electric field and ne changes it is suggested that eia intensification could be triggered by the e field disturbances over the epicenter