weak tidal correlation of nw bohemia vogtland earthquake swarms we analyze the possible effect of solid earth tidal stresses upon a vertical strike slip fault in nw bohemia vogtland central europe typical by occurrence of swarm earthquakes the horizontal components of solid earth tidal stresses were found strongly to prevail and to reach the level of 2 kpa we examined tidal triggering as influence of tidal stresses to launching the swarm activity in relative absence of other stress disturbances the onset times of 46 swarms of mostly ml 3 earthquakes that occurred in the period 1991 2005 displayed an increased occurrence near the fortnightly maximum of tidal extensive normal stress the statistical test however did not prove a statistically significant correlation indicating a triggering effect of fault extension due to tidal loading we also examined tidal effects to the already running seismic activity of the prominent 2000 swarm by comparing the tidal stress distribution in the investigated period with the distribution of tidal stresses in the occurrence times of each earthquake the results show that these distributions are almost similar which indicates that individual earthquakes occur independent of tidal stresses the unclear tidal correlation of the swarm seismicity may be interpreted by small amplitudes and rates of tidal stress changes compared to the amplitudes and rates of coseismic stress perturbations and of pressure bursts of deep generated fluids

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

no clear evidence for localized tidal periodicities in earthquakes in the central japan region we search for possible localized tidal triggering in earthquake occurrence near japan by testing for tidal periodicities in seismicity within a variety of space time bins we examine 74 610 earthquakes of m 3 in the japan meteorological agency jma catalog from january 2000 to april 2013 because we use many earthquakes for which accurate focal mechanisms are not available we do not compute tidal stresses on individual fault planes but instead assume that the mechanisms are likely to be similar enough among nearby events that tidal triggering will promote earthquake occurrence at specific tidal phases after dividing the data into cells at a range of spatial 0 2 0 5 1 0 and temporal dimensions 100 200 400 days we apply schuster s test for non random event occurrence with respect to both the semi diurnal and semi monthly tidal phases because the resulting p values will be biased by temporal clustering caused by aftershocks we apply a declustering method that retains only one event per tidal cycle per phase increment our results show a wide range of p values for the localized earthquake bins but the number of bins with very small p values e g p 0 05 is no more than might be expected due to random chance and there is no correlation of low p value bins with the time of the 2010 m 9 0 tohoku oki earthquake

oxygen isotopic composition of individual olivine grains from the allende meteorite abstract the oxygen isotopic compositions of individual olivine grains from the allende meteorite were determined by ion microprobe techniques a variety of olivine grains were analysed refractory forsterite grains 26 wt rims and twenty eight individual matrix olivine grains 21 41 wt feo in an oxygen three isotope plot refractory forsterite grains 17o 11 18 o 8 fall on the allende mixing line but are significantly less enriched in 16o than spinel and pyroxene from ca al rich inclusions cais possibly indicating a later formation of forsteritic olivine cores of isolated olivine grains with somewhat higher feo contents iogs have oxygen isotopic compositions similar to those of the refractory forsterites 17 o 12 and 18 o 9 both types of olivine grains have oxygen isotopic compositions significantly different from those of chondrules this clearly demonstrates that these olivine grains are not the result of crystallization of chondrule melts fayalite rich rims of the iogs are less enriched in 16o 17 o 3 18 o 0 than the forsteritic cores arguments are presented that this supports a condensation origin of the rims from a gas phase less enriched in 16o than the gas phase from which the forsteritic cores had formed matrix olivines have oxygen isotopic compositions similar to fayalite rich rims however there are variations in the oxygen isotopic composition of matrix olivines that exceed analytical uncertainties suggesting a more complex origin

tidal coulomb failure stresses in the northern andean intermediate depth seismic clusters implications for a possible correlation between tides and seismicity abstract a recent statistical analysis of the relationship between tides and seismic activity in colombia has suggested the existence of correlation anomalies for the case of intermediate depth events in the bucaramanga nest and the cauca cluster moncayo et al 2019 in this work we explore in detail the hypothesis that tides may be triggering seismic activity in these regions and extend the analysis to two other seismic clusters in northern central south america specifically in the areas of el puyo ecuador and pucallpa peru for this purpose we use the available focal mechanism information for seismic events at these locations and calculate for each event the tidal coulomb failure stress tcfs as obtained from estimations of the tidal strain tensor tidal strains are computed considering the earth body tides and the effect of the ocean tidal loading since our purpose is to elucidate the role of tides in earthquake nucleation calculations of the tcfs are conducted not only for the time of earthquake but also for the time of the closest maximum strain within a window of a few hours before the events our results tend to support the hypothesis that tidal stresses are contributing to earthquake generation in all the studied areas this trend is especially stronger when tcfs are calculated at pre earthquake times the physical explanation for the positive contribution of tides to earthquake triggering in intermediate depth clusters may lie in the fact that a wide diversity of fault plane orientations is possible within a relatively small volume of subducted lithosphere so making the tides more likely to help loosening up the blocks at the fault plane to promote slip

tidal triggering of earthquakes in the subducting philippine sea plate beneath the locked zone of the plate interface in the tokai region japan we found a characteristic space time pattern of the tidal triggering effect on earthquake occurrence in the subducting philippine sea plate beneath the locked zone of the plate interface in the tokai region central japan where a large interplate earthquake may be impending we measured the correlation between the earth tide and earthquake occurrence using microearthquakes that took place in the philippine sea plate for about two decades for each event we assigned the tidal phase angle at the origin time by theoretically calculating the tidal shear stress on the fault plane based on the distribution of the tidal phase angles we statistically tested whether they concentrate near some particular angle or not by using schuster s test in this test the result is evaluated by pvalue which represents the significance level to reject the null hypothesis that earthquakes occur randomly irrespective of the tidal phase angle as a result of analysis no correlation was found for the data set including all the earthquakes however we found a systematic pattern in the temporal variation of the tidal effect the p value significantly decreased preceding the occurrence of mz4 5 earthquakes and it recovered a high level afterwards we note that those mz4 5 earthquakes were considerably larger than the normal background seismicity in the study area the frequency distribution of tidal phase angles in the pre event period exhibited a peak at the phase angle where the tidal shear stress is at its maximum to accelerate the fault slip this indicates that the observed small p value is a physical consequence of the tidal effect we also found a distinctive feature in the spatial distribution of p values the small p values appeared just beneath the strongly coupled portion of the plate interface as inferred from the seismicity rate change in the past few years d 2005 elsevier b v all rights reserved

evidence for tidal triggering of earthquakes as revealed from statistical analysis of global data 1 we observe tidal triggering of earthquakes by measuring the correlation between the earth tide and earthquake occurrence we used the times locations and focal mechanisms of the 9350 globally distributed earthquakes with magnitude 5 5 or larger from the harvard centroid moment tensor catalog the tidal stress was theoretically computed by using the preliminary reference earth model and a recent ocean tide model nao 99b we considered the shear stress on the fault plane and the trace of stress tensor j1 defining the tidal phase angle at the occurrence time for each earthquake we statistically tested the phase selectivity using the schuster s method for all the earthquakes no significant correlation is found between the earth tide and earthquake occurrence both for the shear stress and for j1 by classifying the data set according to fault types however we find a high correlation with the shear stress for reverse fault type the correlation is particularly clear for shallow and smaller earthquakes of this type significant correlation with j1 also appears for larger earthquakes of reverse fault type and for shallow and larger ones of normal fault type we find no correlation for strike slip type for all the cases of high correlation earthquakes tend to occur when the tidal stress accelerates the fault slip indicating that high correlation is not coincidental but is physically justified this result strongly suggests that a small stress change due to the earth tide encourages earthquake occurrence when the stress in the future focal area is near a critical condition

influence of fortnightly tides on earthquake triggering at the east pacific rise at 9 50 n the study of tidal forcing provides an opportunity to view the response of the solid earth to known changes in stress earthquakes triggered by diurnal and semidiurnal tidal forces have been well documented for the deep ocean and some terrestrial environments however few studies examine the influence of fortnightly tides on earthquake triggering and only in terrestrial environments we assess triggering of microearthquakes related to true fortnightly tides and fortnightly tidal modulations along the east pacific rise at 9 50 n where strong diurnal and semidiurnal triggering of earthquakes has been observed an ocean bottom seismograph experiment collected microearthquake data between october 2003 and january 2007 a time period that included a well documented submarine eruption culminating in january 2006 we examine how triggering changed through the build up to and aftermath of this seafloor spreading event results show that earthquakes occur preferentially during times of increasing peak volumetric stress leading up to the eruption with strong statistical significance schuster test p values up to 2 22e 31 however the correlation loses its strength immediately prior to and during the eruptive period p value as high as 0 2837 when competing tectonic and magmatic stresses may occur post eruption triggering reappears p value 1 45e 26 but with opposite phase statistical significance is also explored using monte carlo method highlighting limitations of swarm dominated time series for the schuster test nevertheless the observations are consistent with a shift in the dominating stress triggering the earthquakes from extensional tectonics to magmatic processes followed by a post eruption period of cooling relaxation and possibly magma chamber refilling

comment on tidal synchronicity of the 26 december 2004 sumatran earthquake and its aftershocks by r g m crockett et al 1 crockett et al 2006 report a striking coincidence of some of the larger recent earthquakes around the sunda andaman java trench regions with the times of the full and new moon however it may be worth noting that the results contradict nearly all previous studies and theoretical expectations and the statistics invoked have some problems 2 two flavors of earthquake tide correlations have been sought with either the diurnal stress variations or the biweekly modulations in the amplitude of the stress envelope a correlation with both tidal periods has occasionally been noted in the case of seismicity just below the ocean floor at mid ocean ridges but in each reported case the correlation with biweekly tides was much weaker than the correlation with diurnal tides wilcock 2001 tolstoy et al 2002 extensive data on global tectonic earthquakes have sometimes shown evidence of a correlation with diurnal tides tanaka et al 2002 tsuruoka et al 1995 especially in the case of the strongest tides cochran et al 2004 however none of the studies report seeing a correlation with the biweekly tide even regional studies of far larger sets of earthquakes in the san francisco bay area mcnutt and heaton 1981 kennedy et al 2004 and the pacific northwest kennedy et al 2004 find no measurable correlation as stated by hartzell and heaton 1989 the difference in the amplitude of the biweekly tidal stress envelope is much smaller than the diurnal peak to peak stress variation with diurnal stress variation being over 5 times larger than the biweekly variation along the same vein theoretical studies predict a correlation with the diurnal but not biweekly tides due to the small overall amplitude variation of biweekly tides dieterich 1987 3 crockett et al 2006 base their conclusions on a comparison with the lunar phase only however it has been well documented for example in a review by emter 1997 that the tidal time series must be computed in relation to the focal mechanism to derive a useful correlation in addition crockett et al 2006 do not include the ocean tide component of the tidal stress in their correlation even though the ocean tide component is often an order of magnitude larger than the solid earth tide in subduction zone coastal environments depth matters as well for example tsuruoka et al 1995 show that tides calculated at the surface can be opposite in phase to tidal time series at hypocentral depths when ocean loading is taken into account 4 perhaps most importantly the statistics employed by crockett et al 2006 are somewhat problematic schuster s test is only valid for independent datasets in which events occur at random this test can produce a false positive result if the data set is not random and so should not be used for statistical tests on catalogs that include aftershocks therefore the statistics given by crockett et al 2006 for the raw clustered catalog are invalid specifically in the clustered catalog the times of aftershocks of the m9 3 megathrust dominate the sample and they are not uncorrelated in time rather they tend to occur just after the mainshock as aftershocks are prone to do 5 the most compelling statistic of crockett et al 2006 is the one derived from 13 14 declustered events happening near the quadrants of either the full or new moons an only 1 in a 100 chance of finding the result at random is cited but the paper documentation suggests the degrees of free

tidal synchronicity of the 26 december 2004 sumatran earthquake and its aftershocks 1 the frequency of earthquake incidence along the andaman sunda java trench plate boundary region has been investigated for the ten lunar month period 28 october 2004 19 august 2005 encompassing the 26 december 2004 earthquake during this period variations in earthquake activity correlate with the tidal force cycles maxima in earthquake activity occur around the times of new and full moons typically lagging by 0 3 days this relationship is consistent with earthquake inducement via ocean tidal loading also during this period the earthquake incidence associated with new and full moons at the western end of the region was a 38 and b 86 higher than the period averages for the full and declustered major earthquake catalogs respectively

the fortnightly tide and the tidal triggering of earthquakes in this paper we test the southern california network earthquake catalog and the world wide earthquake catalog for a fortnightly tidal periodicity and find none in studies that test the hypothesis of tidal triggering of earthquakes it is usually necessary to resolve the tidal shear stress onto the plane of the fault and in the direction of the slip vector to determine if the stress is compatible with the fault motion heaton 1975 1982 this analysis requires accurate focal mechanisms and knowledge of the focal plane on which slip occurred for as many earthquakes as possible to improve the statistical sampling of the data set however if we consider the fortnightly tide which is a simple amplitude modulation focal mechanism information is not required our analysis assumes that we have a large data base of earthquakes with varying mechanisms the alignment of the slip vector with the tidal shear stress will vary from earthquake to earthquake however if tidal triggering of earthquakes does occur more earthquakes should be triggered out of the total population when the tidal stress is large than when it is small if the largest semi diurnal tide is normalized to an amplitude of 1 0 the fortnightly tide would have an amplitude of 0 17 on this scale and a period of about 2 weeks munk and macdonald 1960 therefore the effect on the occurrence of earthquakes by the tidal shear stress will be modulated with a 2 week period considering the fortnightly tide allows us to utilize entire catalogs of data to test the tidal triggering hypothesis without knowledge of the focal mechanisms

tidal triggering of earthquakes in the northeast pacific ocean summary there have been many searches for evidence of tidal triggering in earthquake catalogues with the exception of volcanically active regions the more rigorous studies in continental settings tend to find no correlation or only a very weak correlation in the oceans the effect of loading by the ocean tides can increase tidal stresses by about an order of magnitude over continental settings in recent years several studies have reported evidence of tidal triggering in oceanic regions and such observations can represent a useful constraint on models of earthquake rupture in this paper i systematically search for a link between ocean tide height and the incidence of earthquakes in the northeast pacific ocean a region of high amplitude open ocean tides the focal mechanisms of most of the earthquakes in these catalogues are unknown but it can be shown that tidal stresses will in most instances promote failure at low tides i investigate three declustered data sets comprising 1 earthquakes from 1980 to 2007 on the juan de fuca plate and in the queen charlotte fault region from land based catalogues 2 earthquakes from 1992 to 2001 on the juan de fuca plate located with the us navy s sound surveillance system sosus hydrophone array and 3 earthquakes from 1980 to 2001 south of alaska and the aleutians located with land based networks i look at the distributions of earthquakes with ocean tide phase height and tidal range and apply schuster and binomial tests and monte carlo simulations to determine if they deviate significantly from random the results show no evidence of triggering during intervals of increased tidal range but all three data sets show a significant increase in earthquake incidence at low tides the signal is particularly strong in the land based catalogue for the juan de fuca plate and queen charlotte fault regions where there is a 15 per cent increase in the rate of seismicity within 15 of the lowest tides the signal is weakest in the sosus data set which may reflect the lower average tidal range at epicentres in this data set or an analysis that is influenced by gaps in the catalogue the triggering signal in the alaska aleutian may be partially obscured by earthquakes in the aleutians where the total tidal stresses can be significantly out of phase with the ocean tide height the increase in the rates of seismicity i observe at low tides is less than observed by local networks on mid ocean ridges similar to the prediction from an analysis of global thrust earthquakes and greater than inferred by extrapolating laboratory simulations of fault failure under tidal loading

evidence of electrical anisotropic structures in the lower crust and the upper mantle beneath the rhenish shield abstract we present the results of a long period electromagnetic investigation of the crust and upper mantle beneath the rhenish shield in western germany the magnetotelluric phase data reveal a frequency dependent regional strike that varies only smoothly across the array at short periods t 1000 s there is a consistent striking in we direction which provides strong evidence of an anisotropic structure in the upper mantle too geomagnetic data were also used whereas we reference the magnetic field components of all sites to an arbitrarily chosen field site that provides a direct view of the anomalous current flow we show that in case of a non one dimensional electrical substructure of the reference site all magnetic transfer functions of the other sites can be affected by lateral conductivity contrasts beneath the reference site a simple method to remove such effects is introduced applying this method the magnetic data show a distinct anomaly in the northwestern part of the area finally we present a 3d model of the conductivity structure beneath the rhenish shield which contains a superposition of two anisotropic structures in the lower crust 2000 s and the upper mantle 20 000 s respectively and a local anomaly in the upper crust 4000 s

can free oscillations trigger foreshocks that allow earthquake prediction the earthquake prediction model of whiteside and ben zion 1995 was examined to ascertain whether or not their proposed method generates statistically significant results their model suggests a remarkable increase in the triggering of small earthquakes by free earth oscillations before some large events in the vicinity of the mainshock months prior to the large event we independently devised a program to reproduce their method and found the results to be dependent upon the number of events used in the generation of triggering percentages results generated using real and random data were nearly identical we devised a parameter to remove sampling bias and test the null hypothesis i e that the results using real data are no different from what is expected for random chance the null hypothesis is upheld and there is no observed increase in this parameter in the location of the loma prieta earthquake prior to that event

tidal triggering of earthquakes analysis of the tidal stress tensor at the time of moderate to large earthquakes strongly suggests that shallow 30 km larger magnitude oblique slip and dip slip earthquakes are triggered by tidal stresses no corresponding triggering effect is seen for shallow strike slip earthquakes or for any type of intermediate or deep focus earthquakes which have been studied tidal triggering is also discussed from the viewpoint of the dilatancy diffusion model specifically the model as usually stated excludes the possibility of small earthquakes being tidally triggered

distribution of the lunisolar tidal elastic stress tensor components within the earth s mantle a set of second order spheroidal love shida numbers h r k r l r and their radial derivatives were determined for the case of a symmetric non rotating elastic isotropic snrei earth with a liquid core by these means the stress tensor components from the surface to the core mantle boundary cmb were calculated for the case of zonal tesseral and sectorial tides the possible dependence of geophysical phenomena on the lunisolar effect is discussed for the three different kinds of tides the case of tidal triggering of earthquakes is discussed in more detail since the tidal potential and its derivatives are coordinate dependent and the zonal tesseral and sectorial tides have different distributions on and within the earth the lunisolar stress cannot influence the break out of every seismological event in the same degree a correlation between earthquake energy release and the lunisolar effect can exist in some cases where the seismic area is well determined and has either one seismic source or severe similar ones particularly in volcanic areas where the seismic activity is connected to the volcano s activity or in the case of some aftershock swarms significant correlation was found by different authors