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

ground zoning against seismic hazard in athens greece abstract the 1999 ms 5 9 athens earthquake caused serious structural damage to buildings in the western part of athens greece this paper presents the ground zoning against seismic hazard proposed shortly after the earthquake in order to aid reconstruction of the area existing engineering geological and geotechnical data were combined with local observations to provide a unified set of classification criteria consistent with provisions of the greek seismic code eak the accuracy and the possible limitations of this zoning procedure are addressed through comparison with observed damage distribution as well as results from seismic ground response analyses performed at sites with well established soil profiles there is clear evidence that the proposed zones correspond to geological formations exhibiting grossly different seismic response with regard to the design of common engineering structures however the mostly qualitative nature of the guidelines for ground categorisation provided by eak and the general lack of systematic site specific geotechnical data for the whole area induce uncertainties in the definition of the seismic design actions for the different zones these objective uncertainties certainly demand increased conservatism but do not limit application of the proposed methodology for first aid preliminary planning in the event of destructive earthquakes

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

seismoionospheric gps total electron content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake 1 the global ionospheric map gim is used to observe variations in the total electron content tec of the global positioning system gps associated with 35 m 6 0 earthquakes that occurred in china during the 10 year period of 1 may 1998 to 30 april 2008 the statistical result indicates that the gps tec above the epicenter often pronouncedly decreases on day 3 5 before 17 m 6 3 earthquakes the gps tec of the gim and electron density profiles probed by six microsatellites of formosat3 cosmic f3 c are further employed to simultaneously observe seismoionospheric anomalies during an mw7 9 earthquake near wenchuan china on 12 may 2008 it is found that gps tec above the forthcoming epicenter anomalously decreases in the afternoon period of day 6 4 and in the late evening period of day 3 before the earthquake but enhances in the afternoon of day 3 before the earthquake the spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions respectively the f3 c results further show that the ionospheric f2 peak electron density nmf2 and height hmf2 significantly decreases approximately 40 and descends about 50 80 km respectively when the gps tec anomalously reduces

a simplified analysis of the total seismic hazard in italy abstract total seismic hazard assessment i e the base hazard modified by local site conditions plays a key role in seismic risk prevention and mitigation this is an important topic due to the impact of a reliable hazard assessment on the resilience of local communities in the case of an earthquake this paper presents a study that evaluates the total seismic hazard for the entire italy excluding the island of sardinia the results are expressed in terms of amplification factors and total hazard parameters to this end soil characterisation was performed firstly using italian seismic network data for 259 sites uniformly distributed across italy and secondly using the mean value of the shear wave velocity available from a global dataset produced by the united states geological survey the amplification effects were quantified according to i an approach consistent with the italian building code and ii one dimensional site response analyses these two procedures are referred to as parsimonious and rigorous here respectively the results indicate a generally satisfactory match between the estimates obtained by means of these two procedures for periods lower than 0 5 s while parsimonious procedures at periods longer than 0 5 s provide an upper limit on the total seismic hazard finally a seismic classification in terms of the classes of total hazard parameters is proposed for the italian peninsula area

a statistical study of ionospheric earthquake precursors monitored by using equatorial ionization anomaly of gps tec in taiwan during 2001 2007 abstract in this paper we examine pre earthquake ionospheric anomalies by the total electron content tec derived from a ground based receiver of the global positioning system gps a network of eight gps receivers is used to construct daily latitude time tec ltt plots to monitor the crest of equatorial ionization anomaly eia in the taiwan area three parameters of the strength location and formation time of the eia crest are extracted a 15 day running medians of the three parameters and the associated upper and lower quartiles are utilized as the references for identifying abnormal signals for all of the 150 m 5 0 earthquakes in the taiwan area during 2001 2007 results show that the eia crest significantly moves equatorward poleward and appears in an earlier later time of the afternoon period a few days before after the earthquakes along the taiwan longitude the two parameters of the eia crest location and occurrence time can be employed to detect ionospheric earthquake precursors the results further imply that atmospheric electric fields generated around the epicenter of a forthcoming earthquake during the preparation period are essential

a fracture arrest model for unconfined dry slab avalanches a simplified model of an unconfined dry snow slab is used to derive expressions for the rate at which elastic strain energy is released and for the fracture resistance during the propagation of the rapid brittle fractures that result in slab avalanches a relatively constant energy release rate is derived based on arguments that associate most of the released energy with the crown fracture in contrast advancing basal and crown fractures result in increasing fracture resistance by assuming fracture propagation will stop when the strain energy release rate is just greater than the fracture resistance the width of a slab avalanche is found to be proportional to an arrest parameter this parameter includes the slab thickness slab tensile strength and basal shear strength each of which can be measured prior to avalanching it is argued that compared to the three variables which can be measured the remaining variables have limited influence on the width of unconfined slab avalanches these less influen

statistical evidences of seismo ionospheric precursors applying receiver operating characteristic roc curve on the gps total electron content in china abstract evidence of the seismo ionospheric precursor sip is reported by statistically investigating the relationship between the total electron content tec in global ionosphere map gim and 56 m 6 0 earthquakes during 1998 2013 in china a median based method together with the z test is employed to examine the tec variations 30 days before and after the earthquake it is found that the tec significantly decreases 0600 1000 lt 1 6 days before the earthquake and anomalously increases in 3 time periods of 1300 1700 lt 12 15 days 0000 0500 lt 15 17 days and 0500 0900 lt 22 28 days before the earthquake the receiver operating characteristic roc curve is then used to evaluate the efficiency of tec for predicting m 6 0 earthquakes in china during a specified time period statistical results suggest that the sip is the significant tec reduction in the morning period of 0600 1000 lt the sip is further confirmed since the area under the roc curve is positively associated with the earthquake magnitude

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

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

on the fracture toughness of snow the release of a dry snow slab avalanche involves brittle fracture it is therefore essentially a non linear fracture mechanics problem traditional snow stability evaluation has mainly focused on snow strength measurements fracture toughness describes how well a material can withstand failure the fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity and hence snow slope stability fracture toughness in tension kic and shear kiic was determined with notched cantilever beam experiments in a cold laboratory measurements were performed at different temperatures and with different snow types of density 100 300 kg m 3 corresponding to typical dry snow slab properties the fracture toughness in tensionkic was found to be larger by about a factor of 1 4 than in shear kiic typical values of the fracture toughness were 500 1000 pa m 1 2 for the snow types tested this suggests that snow is one of the most brittle materials known to man a power law relation of toughness kic on relative density was found with an exponent of about 2 the fracture toughness in tensionkic decreased with increasing temperature following an arrhenius relation below about 8 c with an apparent activation energy of about 0 16 ev above 6 c the fracture toughness increased with increasing temperature towards the melting point i e the ar rhenius relation broke down the key property in dry snow slab avalanche release the critical crack size under shear at failure was estimated to be about 1m

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

preseismic ionospheric anomalies detected before the 2016 kumamoto earthquake on 15 april 2016 the kumamoto earthquake mw 7 3 occurred in japan with no warning signals global navigation satellite system gnss receivers provide useful information on disturbances in the ionosphere by calculating the changes in total electron content tec which is the number of electrons in the ionosphere here we show our recently proposed correlation analysis of tec data which can detect the preseismic ionospheric anomalies from the public gnss data our method detected the ionospheric anomaly several tens of minutes before the 2016 kumamoto earthquake near its epicenter furthermore we gave an indicator to distinguish between the preseismic tec anomalies and the medium scale traveling ionospheric disturbances mstids by calculating the anomalous area rates these results support the hypothesis for existence of the preceding phenomena before large earthquakes

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

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

the critical size of macroscopic imperfections in dry snow slab avalanche initiation 1 dry snow slab avalanches initiate after mode ii fracture propagation within a thin weak layer under a planar slab dry alpine snow in which avalanches form is a porous material typically with volume fraction filled by solids of between 10 and 50 if snow slab avalanches were caused by small scale flaws there would be continuous avalanches and alpine snow would not survive on steep slopes instead snow slab avalanches initiate from macroscopic imperfections or weak zones within the weak layer these are called sweet spots by practitioners and deficit zones in the pioneering work by conway and abrahamson in the 1980s in this paper the results of 750 in situ shear fracture tests from 68 slab weak layer combinations are summarized in relation to the critical sweet spot length and weak layer crystal form the results show that the critical sweet spot lengths follow a gamma probability density function with a range from 0 14 to 1 3 m and most probable value 0 5 m the results also imply that critical sweet spot length depends on weak layer grain type with significantly larger values for persistent forms surface hoar and facets than for nonpersistent forms decomposing and fragmented grains

solitary fracture waves in metastable snow stratifications 1 fracture processes in layered snow have many implications on avalanche hazard and mountain safety this paper is a contribution for a better understanding of fracture dynamics in a stratified medium with a collapsible layer in terms of a simple analytical model involving only field measurable parameters for this purpose a simple three layer snow stratification is considered to consist of a compact basal layer a collapsible weak layer and a homogenous top layer it is shown analytically that the fracture of the weak layer can occur in the form of a localized disturbance zone propagating a collapse with constant velocity and wavelength simple analytical expressions describing the disturbance are obtained the results are in good agreement with observations in the terrain the presented fracture process is relevant to the release of dry snow slab avalanches and to the propagation of firn quakes and whumpfs but may also apply to other stratified media with appropriate properties

spatial and temporal characteristics of the microseismicity preceding the 2016 m l 6 6 meinong earthquake in southern taiwan before the ml 6 6 meinong earthquake in 2016 intermediate term quiescence qi foreshocks and short term quiescence qs were extracted from a comprehensive earthquake catalog in practice these behaviors are thought to be the seismic indicators of an earthquake precursor and their spatiotemporal characteristics may be associated with location magnitude and occurrence time of the following main shock hence detailed examinations were carried out to derive the spatiotemporal characteristics of these meaningful seismic behaviors first the spatial range of the qi that occurred for 96 days was revealed in and around the meinong earthquake second a series of foreshocks was present for 1 day clustered at the southeastern end of the meinong earthquake third qs was present for 3 days and was pronounced after the foreshocks although these behaviors were recorded difficultly because the qi was characterized by microseismicity at the lower cut off magnitude between ml 1 2 and 1 6 and most of the foreshocks were comprised of earthquakes with a magnitude lower than 1 8 they carried meaningful precursory indicators preceding the meinong earthquake these indicators provide the information of 1 the hypocenter which was indicated by the area including the qi foreshocks and qs 2 the magnitude which could be associated to the spatial range of the qi 3 the asperity locations which might be related to the areas of extraordinary low seismicity and 4 a short term warning leading of 3 days which could have been announced based on the occurrence of the qs particularly qi also appeared before strong inland earthquakes so that qi might be an anticipative phenomenon before a strong earthquake in taiwan

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

fracture propagation propensity in relation to snow slab avalanche release validating the propagation saw test 1 the propagation saw test pst was designed to assess the fracture propagation propensity of weak snowpack layers in relation to snow slab avalanche release its predictions were tested against independent field observations of weak layer fracture initiation and slope scale fracture propagation e g avalanche release a total of 170 tests were performed at 23 sites approximately 76 of tests correctly predicted the observed slope scale fracture propagation or lack thereof however 20 of tests predicted that propagation would not occur at sites that had recently propagated fractures the predictive accuracy of the dataset improves if only test columns approximately 1 0 m long are selected critical fracture energy release rate calculations show that the lowest values are found in snowpacks where fractures initiated but did not propagate this suggests that physical descriptions of propagation propensity in weak snowpack layers should include a sustainability term

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

variations in the building site categories in the underground mining region of doubrava czech republic for land use planning abstract in terms of demands and needs of ground investigation and foundation engineering the engineering geological conditions in the underground mining territories represent anthropogenically influenced areas in the most complicated manner since they suffer the impacts from the underground mining of mineral resources the subjects of observation are the so called building site categories which represent a certain risk factor that must be taken into consideration during foundation engineering and engineering geological studies in the undermined territories it is necessary to realise that underground mining is an anthropogenic geodynamic process which significantly varies over time due to mining change and consequently with variations in the position shape and size of subsidence in a subsidence basin all the above mentioned variations should be mandatory knowledge for land use planners engineering geologists geotechnicians foundation engineers and designers because of the evident logicality of these needs this work presents a case study ostrava karvina coal district in the north east of the czech republic of variations in the building site categories over time and the results show that the chronology of the changes has a very significant influence in this area of interest the results of the building site category evaluation imply that the majority of the interest area falls within relatively good conditions for founding all kinds of structures however it was then necessary to consider variations over time in the surface area of less suitable building site categories a trend certainly confirmed the existence of the previously presumed mutual relationship between building site categories and subsidence size distribution it is apparent from the analytic results of the relationship between building site categories and planned development that the negative impacts of mining have been only partly considered or completely disregarded in the development planning process consequently future land use planners should carefully consider these particular building site categories as the most important and significant factors in the undermining of a region in this manner development can be successfully planned for present and future safety

is an unusual large enhancement of ionospheric electron density linked with the 2008 great wenchuan earthquake 1 on 12 may 2008 at 0628 ut a major earthquake ms 8 0 struck wenchuan county 31 0 n 103 4 e in southwest china the maximum ionospheric electron density at f2 peak nmf2 recorded an unusual large enhancement during the afternoon sunset sector by the chinese ionosondes over wuhan 30 5 n 114 4 e and xiamen 24 4 n 123 9 e which are close to the earthquake epicenter an averaged increase at these two stations is about 2 times on a geomagnetic quiet day 9 may kp 2 3 days prior to the earthquake relative to the median value of 1 12 may whereas the increase was much less significant over yamagawa 31 2 n 130 6 e and okinawa 26 7 n 128 2 e in japan combining the data from the network of 58 global positioning system receivers around china and the global ionospheric map the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90 130 e our results suggest that this abnormal enhancement is most possibly a seismo ionospheric signature

fracture mechanical models of dry slab avalanche release experimental evidence shows that snow is a pressure sensitive dilatant strain softening material in slow constant rate shear deformation when strain softening initiates in a weak layer underneath a snow slab avalanche release is hypothesized to be possible with or without additional loading specifically two cases are discussed 1 a shear crack like disturbance can initiate after formation of a slip surface in the weak layer and traverse the layer by a self propagating progressive failure with or even without loading and 2 a self propagating shear instability can develop when a region of the weak layer is driven past peak shear strength by loading for these cases the implied fracture sequence fracture geometry time scale of release and temperature effects are discussed and shown to be consistent with the known facts of dry slab avalanche release

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

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

spatiotemporal characteristics of the geomagnetic diurnal variation anomalies prior to the 2011 tohoku earthquake mw 9 0 and the possible coupling of multiple pre earthquake phenomena abstract xu et al 2013 and han et al 2015 have reported unusual behaviors of geomagnetic diurnal variation gdv in the vertical component prior to the 2011 off the pacific coast of tohoku earthquake mw 9 0 to make a better understanding of this phenomenon temporal spatial analyses of gdv have been applied in this study geomagnetic data of long term observations at 17 stations in japan have been analyzed using the same method in han et al 2015 ratios of diurnal variation range between the reference station kak and the target stations have been computed after removing seasonal variations the 15 day backward running mean values of the ratios in the vertical component shows a clear anomaly exceeding the statistical threshold about 2 months before the mega event at both esa and miz stations in the tohoku region locations of anomalies in spatial distribution show a good correlation with the epicenter of the mw 9 0 earthquake these spatiotemporal results are consistent with those obtained from other independent observations such as groundwater level and gps displacements the coupling of multiple pre earthquake phenomena may help to understand the preparation process of a mega earthquake in the subduction zone

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

field measurements of sintering after fracture of snowpack weak layers 1 this research documents two cases where field workers unintentionally fractured a snowpack weak layer but no avalanche released measurements from before and after the fractures provide unique data sets on the temporal change of snow stability shear strength decreased immediately after fracture on both slopes subsequent strengthening occurred in both cases though the rates differed presumably due to the characteristics of the weak layers our results have two important implications first they suggest the sub critical weak layer fractures assumed as a prerequisite in some snow slab avalanche release models are transient features and future modeling efforts must take this into account second they provide insights into interpreting snow stability tests and assessing the stability of slopes with fractured weak layers

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