interpretation of significant ground response and structure strong motions recorded during the 1994 northridge earthquake abstract some of the largest accelerations and velocities ever recorded at ground response and structural sites occurred during the northridge earthquake these motions are greater than most existing attenuation models would have predicted although the motions are large the correspondence between measured acceleration and damage requires further study since some sites with high acceleration experienced only moderate damage also some peak vertical accelerations were larger than the horizontal but in general they are smaller and fit the pattern observed in previous earthquakes strong motion records processed to date show significant differences in acceleration and velocity waveforms and amplitudes across the san fernando valley analysis of processed data from several buildings in the san fernando valley indicates that short period buildings such as shear wall buildings experienced large forces and relatively low inter story drift during the northridge earthquake however long period 1 to 5 sec steel or concrete moment frame buildings experienced large inter story drift for this earthquake accelerations did not always amplify from base to roof for flexible structures like the moment frame buildings but the displacements were always larger at the roof the drifts at many of the moment frame buildings were larger than the drift limit for working stress design in the building code the records from a base isolated building indicate that high frequency motion was reduced significantly by the isolators the isolators deformed about 3 5 cm which is much less than the design displacement the records from a parking structure show important features of the seismic response of this class of structure

the 1999 mw 7 1 hector mine california earthquake sequence complex conjugate strike slip faulting the 1999 m w 7 1 hector mine mainshock showed right lateral strike slip faulting with an initial strike of n6 w and vertical dip the mainshock was preceded within 20 hours by 18 recorded foreshocks of 1 5 m 3 8 within a few kilometers distance of the mainshock hypocenter the aftershocks delineate how the hector mine earthquake ruptured with strike n6 w to the south for a distance of 15 km and possibly to the north for a distance of several kilometers the two largest aftershocks of m 5 9 and m 5 7 occurred near the north and south ends of the first mainshock rupture segment the second segment of rupture starting 15 km to the south away from the mainshock hypocenter delineated by strike slip and thrust faulting aftershocks extends 10 km farther away with a strike of s140 e along the bullion fault the aftershocks also outline an unusual third rupture segment extending from about 5 km south of the hypocenter with a strike of n30 w to n35 w for a distance of 20 km approximately 10 to 25 km farther to the north and west of the mainshock epicenter several clusters form a complex aftershock distribution three dimensional vp and vp vs models of the region exhibit only small regional changes as is typical for the mojave region nonetheless the mainshock rupture started within a region of rapidly varying vp and at least three regions of low vp vs are imaged within the aftershock zone the rate of decay for the hector mine earthquake sequence has been slightly above the mean for both p values and b values in southern california the focal mechanisms of the aftershocks and the state of stress are consistent with strike slip faulting including a component of normal faulting most prominent to the north the orientation of the regional maximum horizontal stress the variation in orientation of the mainshock fault segments by 30 and scattered distribution of aftershocks suggest that the mainshock and aftershock deformation field exhibit volumetric shear deformation accommodated by complex conjugate sets of strike slip faults

shallow velocity structure and poisson s ratio at the tarzana california strong motion accelerometer site the 17 january 1994 northridge california earthquake produced strong ground shaking at the cedar hills nursery referred to here as the tarzana site within the city of tarzana california approximately 6 km from the epicenter of the mainshock although the tarzana site is on a hill and is a rock site accelerations of approximately 1 78 g horizontally and 1 2 g vertically at the tarzana site are among the highest ever instrumentally recorded for an earthquake to investigate possible site effects at the tarzana site we used explosive source seismic refraction data to determine the shallow 70 m p and s wave velocity structure our seismic velocity models for the tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking p wave velocities range from 0 9 to 1 65 km sec and s wave velocities range from 0 20 and 0 6 km sec for the upper 70 m we also found evidence for a local s wave low velocity zone lvz beneath the top of the hill the lvz underlies a cdmg strong motion recording site at depths between 25 and 60 m below ground surface bgs our velocity model is consistent with the near surface 30 m p and s wave velocities and poisson s ratios measured in a nearby 30 m borehole high poisson s ratios 0 477 to 0 494 and s wave attenuation within the lvz suggest that the lvz may be composed of highly saturated shales of the modelo formation because the lateral dimensions of the lvz approximately correspond to the areas of strongest shaking we suggest that the highly saturated zone may have contributed to localized strong shaking rock sites are generally considered to be ideal locations for site response in urban areas however localized highly saturated rock sites may be a hazard in urban areas that requires further investigation

a bayesian iterative geomagnetic model with universal data input self consistent spherical harmonic evolution for the geomagnetic field over the last 4000 years abstract changes of the earth s magnetic field have been observed with varying spatial and temporal resolution since the middle ages by means of compasses and later by refined mechanical inclination and intensity instruments until the modern use of quantum mechanical devices and satellite observations ancient records on the other hand rely on the natural magnetization of archaeological artifacts and other materials such as rocks and sediments being therefore indirect less accurate and sparser the combination of such heterogeneous records into a single self consistent global model of the geomagnetic field is very challenging the highly uneven data coverage both in space and time requires a careful handling of data uncertainties and error correlations previous models dealt with this problem using separated treatments of instrumental data and indirect records respectively as well as a different handling of the dipole field component with respect to non dipole terms here we present a global geomagnetic field model based for the first time on the simultaneous inversion of historical archaeomagnetic and volcanic records using a bayesian approach with minimal committing time regularization that minimizes the energy of secular variation a detailed assessment of data uncertainty and error correlation is used to minimize artifacts generated by the appearance of an overwhelming number of incomplete mostly declination only records associated with shipboard measurements in the early colonial period our model yields lower dipole energies which better match modern values as well as higher non dipole energies and a stronger secular variation of the dipole moment some model artifacts associated with extremely heterogeneous distributions of records in time and space are not completely eliminable and might be caused by incorrect a priori uncertainty assessments alternatively they might represent an intrinsic limit that can be overcome only by adding new records at critical locations and times

archaeomagnetism at ebla tell mardikh syria new data on geomagnetic field intensity variations in the near east during the bronze age abstract thanks to systematic excavations conducted at tell mardikh ebla syria during more than 40 years we collected eleven groups of bronze age ceramic fragments defining a series of seven time intervals dated to between 2300 bc and 1400 bc archaeointensity experiments were performed using the triaxe protocol that takes into account both anisotropy thermoremanent magnetization and cooling rate effects the results complemented by three other data previously obtained from ebla allow the recovery of geomagnetic field intensity variations over nearly 1000 years characterized by a v shape with a distinct relative intensity minimum around the 18th century bc they also permit to constrain the occurrence of an intensity maximum between 2300 and 2000 bc together with other archaeointensity data obtained from syrian levantine and anatolian regions the results from ebla help to make emerging a coherent pattern of geomagnetic field intensity variations in the near east over the entire bronze period this evolution was marked by distinct intensity maxima at 2600 2500 bc 2300 2000 bc 1550 1350 bc and at the very beginning of the first millennium bc iron age the latter showing a much higher magnitude than the three older ones we discuss the fact that the detected geomagnetic field intensity maxima could be associated with the occurrence of archaeomagnetic jerks that appear synchronous within age uncertainties with significant regional climatic fluctuations

geomagnetic intensity spike recorded in high resolution slag deposit in southern jordan article i nfo in paleomagnetism periods of high field intensity have been largely ignored in favor of the more spectacular directional changes associated with low field intensity periods of excursions and reversals hence questions such as how strong the field can get and how fast changes occur are still open in this paper we report on data obtained from an archaeometallurgical excavation in the middle east designed specifically for archaeomagnetic sampling we measured 342 specimens from 72 samples collected from a 6 1 m mound of well stratified copper production debris at the early iron age 12th 9th centuries bce site of khirbat en nahas in southern jordan seventeen samples spanning 200 yr yielded excellent archaeointensity results that demonstrate rapid changes in field intensity in a period of overall high field values the results display a remarkable spike in field strength with sample mean values of over 120 t compared to the current field strength of 44 t a suite of 13 radiocarbon dates intimately associated with our samples tight control of sample location and relative stratigraphy provide tight constraints on the rate and magnitude of changes in archaeomagnetic field intensities

seismic remote sensing for the earthquake source process and near source strong shaking a case study of the october 16 1999 hector mine earthquake a new methodology to automatically determine the earthquake source process and near source strong ground motions using regional and local distance data was used to study the october 16 1999 hector mine earthquake mw7 1 broadband displacement data were inverted for the seismic moment tensor and to resolve the fault plane ambiguity independent of aftershock location and surface faulting information the identified nnw striking fault plane was used to invert for the distribution of fault slip over a planar surface the slip model was used to predict near fault peak ground velocity which was found to agree well with the trinet shakemap and also with near fault observations that were not available at the time of the initial analysis our method if automated is capable of providing near source strong ground motion information within 30 minutes of the earthquake origin time even in cases where there are few near fault recording instruments

environment and collapse eastern anatolian obsidians at urkesh tell mozan syria and the third millennium mesopotamian urban crisis the early to middle bronze age transition in northern mesopotamia has received great attention for the apparent concurrence of aridification deurbanisation and the end of the akkadian empire around 2200 bce our understanding of the crisis has been almost exclusively shaped by ceramics demography and subsistence exchange and the associated social networks have been largely neglected here we report our sourcing results for 97 obsidian artefacts from urkesh a large urban settlement inhabited throughout the crisis before the crisis six obsidian sources located in eastern anatolia are represented among the artefacts such a diversity of eastern anatolian obsidians at one site is hitherto unknown in mesopotamia it implies urkesh was a cosmopolitan city with diverse visitors or visitors with diverse itineraries during this crisis however obsidians came from only two of the closest sources two to three centuries passed before varied obsidians reappeared even when an obsidian source reappears the raw material seems to have come from a different collection spot we discuss the likely exchange mechanisms and related social networks responsible for the arrival of obsidians at urkesh and how they might have changed in response to climatic perturbations and regional government collapse

the effect of cooling rate on the intensity of thermoremanent magnetization trm acquired by assemblages of pseudo single domain multidomain and interacting single domain grains summary experiments designed to measure the absolute palaeointensity of the geomagnetic field generally do so by comparing the ancient thermoremanent magnetization trm retained by an igneous rock with a new trm imparted in the laboratory one problem with this procedure is that the relative magnitudes of the ancient and laboratory trms may be influenced not only by the external field intensities at the time the two coolings took place but also by the rate at which the coolings themselves occurred here we present new measurements of this cooling rate effect obtained from treatments in the laboratory differing in cooling rate by a factor of 200 synthetic samples containing sized ferrimagnetic grains were used in the experiments theoretical considerations and previous experiments have indicated the cooling rate effect to be dependent on domain state increases in trm magnitude of more than 7percent per order of magnitude decrease in cooling rate have been reported for assemblages of non interacting single domain sd grains here we focus on magnetite grains in the less well studied pseudo single domain psd and multidomain md states using a range of applied field intensities to impart the trms for the first time we also measure the cooling rate effect in grains of titanomagnetite that have been oxyexsolved so that they contain strongly interacting sd lamellae in all cases the cooling rate effect measured was in the same sense as alreadyobservedinidealmagneticallynon interactingsdgrainsbutwasconsiderablyweaker on average the effect did not exceed 3percent increase in trm per order of magnitude decrease in cooling rate and did not show any systematic dependence on appliedfield intensity insomesamples containing coarsergrains thecoolingrateeffectwasnotdistinguishablefrom zero the sense and magnitude of the cooling rate effect remain uncertain in truly md grains as different studies have produced discrepant results for the more practically relevant case of psd and interacting sd grains which commonly dominate the trm in igneous rocks however it appears that we can be more confident in our assertions the cooling rate effect in such materials is in the same sense as in non interacting sd grains but smaller a consequence of long range ordering in lavas and small intrusions containing these it is unlikely to exceed 10percent although a correction should always be attempted the results of palaeointensity studies based upon such samples will generally not be severely biased

seismic response of a hill the example of tarzana california the northridge california earthquake that strongly shook the city of los angeles in january 1994 produced one of the highest ground accelerations ever recorded in an earthquake at a site located on top of a small hill in tarzana about 6 km south of the epicenter the subsequent study of aftershock recordings obtained by a dense seismic array deployed on the hill a few days after the earthquake showed the existence of a strong amplification at stations located at the top of the hill relative to stations near the base spudich et al 1996 resonances and polarization rotations were also observed we investigate in this study the role that the topography of the site played on the observed ground motions and accelerations to this aim we perform numerical simulations and study the response of the three dimensional topography of the site to incident shear waves polarized in different directions the method used is a boundary integral equation scheme in which the green s functions are calculated by the discrete wavenumber method the results obtained show that the topography of the site though quite gentle the hill is less than 20 m high strongly affects the ground motions in the frequency range between 2 and 15 hz many of the observed characteristics of the seismic response at tarzana are explained in part by its topography the consistent amplification of ground motion at and near the top of the hill the directional seismic response of the hill that results in a strong amplification of the ground motion transverse to the direction of elongation of the hill the existence of a fundamental transverse oscillatory resonance mode of the hill at 3 to 5 hz the rotation of the polarization of ground motion and the spatial variation of amplification over the hill at the fundamental resonance mode the seismic response of the topography however does not fully explain the amplitude of the effects observed the three dimensional geological structure of the site must in some way amplify the effect of the topography to produce the observed seismic response in spite of not being as strong as the observed effect the topographic effect of the site is considerable the ground motion is amplified by factors ranging from 30 to 100 at some locations in the frequency range from 2 to 15 hz rapid spatial variations of ground shaking intensities can take place over distance scales of a few tens of meters at high frequency finally the results of the simulation indicate that the topography of the site amplified the large east west accelerations recorded there during the northridge mainshock by 30 to 40

full vector archaeomagnetic records from anatolia between 2400 and 1350 bce implications for geomagnetic field models and the dating of fires in antiquity abstract anatolia as one of the busiest crossroads of ancient civilizations provides an ideal platform for archaeomagnetic studies previous results from the middle east have suggested the occurrence of a strong peak in geomagnetic intensity at 1000 bce associated with dramatic field strength variations that could require a radical rethinking of geodynamo theory the behavior of the field in the centuries preceding this peak remains poorly constrained however here we present the results of full vector archaeomagnetic experiments performed on 18 sets of samples from three archaeological sites belonging to assyrian trade colony and hittite periods associated rock magnetic analyses showed that the major magnetic carrier is magnetite chemically stable up to 700 c and the magnetic mineral assemblage is composed mostly of non interacting psd grains the directional results are compared with existing data and with the most recent global geomagnetic field models pfm9k 1b and sha dif 14k the directions are in remarkably good agreement with sha dif 14k which is based on archaeomagnetic and lava flow data together with our earlier results from anatolia we triple the existing database of directions for the 700 year long period 2200 1500 bce over a large region from greece to azerbaijan and from moldavia ukraine to egypt three archaeointensity methods thermal izzi thellier microwave thellier and the multi specimen protocol msp produced virtual axial dipole moment estimates 9 0 10 9 10 22 am 2 that are somewhat higher than contemporaneous regional and global data and model predictions suggesting that the field was already substantially stronger than today more than 800 years prior to the reported peak in addition to constraining geomagnetic variability our data also allow us to assign relative dates to inferred fire events in the assyrian trade colony period sites this allows us to conclude that the fire events at the largest site kultepe were not all contemporaneous with one another and with the abandonment of the site as has been previously hypothesized

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

far source long period displacement response spectra in the po and venetian plains italy from 3d wavefield simulations abstract design elastic displacement spectra for seismic codes and zoning studies of seismic hazard for long period structures are becoming of utmost importance in modern earthquake engineering the increase of displacement based design approaches together with the availability of good quality digital strong motion data allow the creation of reliable spectral shapes for seismic design of up to 10 s nevertheless to characterize the site amplification effects during large levels of shaking additional studies are needed especially in deep sedimentary basins and plains that can be strongly excited by large amplitude long period waves data within deep basins is rare because accelerometric seismic networks are normally deployed on rock or stiff soil and modeling of waveforms is hence necessary for bridging this gap focusing on the numerical modeling of the 3d wavefield in 1d flat layered and 3d structures in the po and venetian plains northern italy and on earthquakes with magnitudes m 6 6 and hypocentral distances greater than 50 km in this study we 1 estimate the displacement response spectra drs from 1 to 10 s in the po and venetian plains 2 compare the drs from numerical simulations using flat layered and heterogeneous 3d models against the currently available uniform hazard drs for italy and 3 evaluate the influence of deep sediments on drs shape and thus on seismic codes finally 1d and 3d simulated drs are compared with drs obtained from recordings in the kanto basin where similar long period displacement is observed

further evidence of the levantine iron age geomagnetic anomaly from georgian pottery recent archaeomagnetic data from ancient israel revealed the existence of a so called levantine iron age geomagnetic anomaly liaa which spanned the first 350 years of the first millennium before the common era b c e and was characterized by a high averaged geomagnetic field virtual axial dipole moments vadm 140 z am2 nearly twice of today s field short decadal scale geomagnetic spikes vadm of 160 185 z am2 fast field variations and substantial deviation from dipole field direction the geographic constraints of the liaa have remained elusive due to limited high quality paleointensity data in surrounding locations here we report archaeointensity data from georgia showing high field values vadm 150 z am2 in the tenth or ninth century b c e low field values vadm 60 z am2 in the twelfth century b c e and fast field variation in the fifth and fourth centuries b c e high field values in the time frame of liaa have been observed so far only in three localities near the levant eastern anatolia turkmenistan and now georgia all located east of longitude 30 e west of this in the balkans field values in the same time are moderate to low these constraints put geographic limits on the extent of the liaa and support the hypothesis of an unusually intense regional geomagnetic anomaly during the beginning of the first half of the first millennium b c e comparable in area and magnitude but of opposite sign to the presently active south atlantic anomaly

refining the archaeomagnetic dating curve for the near east new intensity data from bronze age ceramics at tell mozan syria abstract uncertainty in radiocarbon dates for the near east caused by a bimodal distribution of ages due to the natural fluctuations of 14 c in the atmosphere has demonstrated the need for an alternative absolute dating technique to aid in the construction of site chronologies here we present a new archaeointensity reference curve model for the first three millennia bce for the levant syria israel jordan for use in archaeomagnetic dating and contribute twelve new intensity results to an increasingly dense geomagnetic field record for the period between 2400 and 1200 bce in the near east archaeomagnetic analysis was conducted on ceramic samples i e pottery sherds from seven sequential and well constrained occupational layers at the site of tell mozan bronze age urkesh in northeastern syria resulting in a 90 success rate by specimen n 42 for archaeointensity determination and an 86 correspondence between the model and the archaeologically derived dates within one standard deviation 1 age standard deviations as low as 24 years were obtained after integration with stratigraphic constraints we also outline the techniques and sampling procedures of archaeomagnetic dating in a manner suitable for the non paleomagnetist while detailing methodology for archaeomagnetic researchers

primary surface rupture associated with the mw 7 1 16 october 1999 hector mine earthquake san bernardino county california the m w 7 1 hector mine earthquake occurred within the mojave desert portion of the eastern california shear zone and was accompanied by 48 km of dextral surface rupture complex northward rupture began on two branches of the lavic lake fault in the northern bullion mountains and also propagated southward onto the bullion fault lesser amounts of rupture occurred across two right steps to the south surface rupture was mapped using postearthquake 1 10 000 scale aerial photography field mapping provided additional detail and more than 400 fault rupture observations of these approximately 300 measurements were used to characterize the slip distribution en echelon surface rupture predominated in areas of thick alluvium whereas in the bedrock areas rupture was more continuous and focused within a narrower zone measured dextral offsets were relatively symmetrical about the epicentral region with a maximum displacement of 5 25 0 85 m 1 vertical slip was a secondary component and was variable with minor west side down displacements predominating in the bullion mountains field and aerial photographic evidence indicates that most of the faults that ruptured in 1999 had had prior late quaternary displacement although only limited sections of the rupture show evidence for prior holocene displacement 1 fn 1

geomagnetic field intensity behavior in the middle east between 3000 bc and 1500 bc 1 an archeointensity study was carried out on 14 sites of syrian baked clay artifacts archeologically dated between 2500 bc and 1600 bc using an experimental protocol involving high temperature magnetization measurements well defined mean intensity values were derived for 13 different sites with three to nine results obtained at the fragment level per site results of similar ages are coherent and the new data set is in good agreement with previous archeointensity results obtained from the same region all together these data allow one to refine the evolution of the geomagnetic field intensity in the middle east during the third and the second millennium bc in particular they show the occurrence of three periods of rather sharp intensity increase at 2600 bc 2200 bc and 1600 bc possibly at the times of climatic cooling in the eastern north atlantic further suggesting a connection between the earth s magnetic field and multi decadal climatic events

peak accelerations from the 1992 landers and big bear california earthquakes peak ground accelerations pga at 181 sites for the landers mw 7 3 earthquake and at 85 sites for the big bear mw 6 2 aftershock are compared to the joyner and boore 1988 jb attenuation relationships and examined for spatial variations this study finds the following five results first at the 95 confidence level the mean of pga values for both earthquakes is significantly higher than the jb median by a factor near 2 second for distances greater than 70 km the observations from the landers earthquake indicate that attenuation of ground motion with distance is less than that predicted by geometric spreading and by jb third the northward propagation of the landers rupture significantly reduces pga values recorded at strong motion stations south of the epicenter fourth stations in the los angeles basin and the coachella valley recorded higher pga values than expected during both events finally site geology using the site classification scheme of jb generally does not have a statistically significant effect on pga except in the distance range from 60 to 100 km for the landers earthquake the observed difference between soil and rock site pga s between 60 and 100 km for the landers data set may be a combination of higher values of pga recorded at soil sites in basins an s wave radiation maximum in the san bernardino area and directivity effects

analysis of geomagnetic field intensity variations in mesopotamia during the third millennium bc with archeological implications abstract we present new archeointensity results obtained at two multi layer archeological sites tell atij and tell gudeda northeastern syria dated from the early bronze period in the third millennium bc the archeointensity data were obtained using the experimental protocol developed for the triaxe magnetometer in total 68 fragments 204 specimens of 151 fragments analyzed passed our selection criteria allowing average intensity values to be estimated for 14 archeological layers nine at tell atij and five at tell gudeda based on the available archeological constraints the different archeological layers of tell atij and tell gudeda were dated between 2900 bc and 2600 bc and between 2550 bc and 2325 bc respectively the tell atij data show a significant increase in intensity over the dated period while the results from tell gudeda exhibit a v shape evolution using high quality data available from syria the levant and turkey a regional geomagnetic field intensity variation curve spanning the entire third millennium bc was constructed using a trans dimensional bayesian method it clearly shows two intensity peaks around 2600 bc and at 2300 bc associated with variation rates of 0 1 0 2 t yr this indicates that the occurrence of century scale intensity peaks with rates of variation comparable to or even slightly higher than the maximum rates observed in the modern geomagnetic field is an ubiquitous feature of the geomagnetic secular variation from an archeological point of view the new archeointensity data strengthen the hypothesis that the successive occupation of tell atij and tell gudeda was synchronous with the two first urban phases of mari making possible a sustained trade network between these settlements during the third millennium bc we further suggest that the end of mari s first urban phase contemporaneous with the abandonment of tell atij might have been caused by a regional drought episode around 2600 bc more generally the bayesian approach used to estimate the new reference intensity variation curve offers promising chronological constraints for archeological purposes

reconstructing the holocene geomagnetic field abstract knowledge of the holocene evolution of earth s magnetic field is important for understanding geodynamo processes in the core is necessary for studying long term solar terrestrial relationships and can provide useful age constraints for archeologicaland stratigraphic applications continuous time varying global field models based on archeo and paleomagnetic data are useful tools in this regard we use a comprehensive data compilation and recently refined modelling strategies to produce cals10k 1b the first time varying spherical harmonic geomagnetic field model spanning 10 ky the model is an average obtained from bootstrap sampling to take account of uncertainties in magnetic components and ages in the data and hence has version number 1b instead of 1 this model shows less spatial and temporal resolution than earlier versions for 0 3 ka and particularly aims to provide a robust representation of the large scale field at the core mantle boundary cmb we discuss the geomagnetic dipole evolution and changes in holocene magnetic field morphology at the cmb as shown by the new reconstruction the results are compatible with earlier models cals3k 3 and cals3k 4 for 0 3 ka but reveal some clear deficiencies in the 0 7 ka cals7k 2 model prior to 3 ka cals10k 1b is able to resolve mobile and structurally evolving high latitude radial field flux lobes at the cmb in both hemispheres as well as persistent non zonal structure in the 10 ky average contributions to the average field from time varying structures in the equatorial indonesian australian region are particularly striking

regions of reduced static stress drop near fault tips for large strike slip earthquakes abstract we present a case study of slip distributions for the 1992 landers m w 7 3 and the 1999 hector mine m w 7 1 earthquakes in california s mojave desert slip distributions as determined from geophysical inversion of geodetic strong ground motion and teleseismic data are complex heterogeneous and often exhibit linearly tapering or concave upward patterns toward segment tips distinctly different from the elliptical slip distributions characteristic of uniform stress drop mechanical interaction of discontinuous fault segments fully explains the reduced slip near the southern termination of the camp rock emerson fault segment of the landers rupture however numerical models demonstrate that such interactions are insufficient to explain slip distributions observed at other segment terminations numerical models demonstrate that long 5 25 km zones of reduced stress drop in the vicinity of some rupture segment terminations can explain the slip distributions for these large earthquakes zones of reduced stress drop are implemented as regions of increased coulomb strength slip distributions are improved 30 70 relative to models with uniform stress drop regions of reduced stress drop appear to play a relatively greater role near segment tips at which rupture terminates than near segment tips at which rupture jumps to a nearby fault segment similar results are obtained implementing discrete stepwise and spatially linear reductions of stress drop plausible mechanical explanations for such zones of reduced stress drop include heterogeneous fault strength or friction spatial or temporal changes in pore pressure geometric complexity of the fault surface heterogeneity of normal tractions resolved on the fault surface inelastic deformation and dynamic rupture effects

climatology of intrusions into the tropical upper troposphere regions of upper tropospheric equatorial westerly winds observed over the pacific and atlantic oceans during northern fall to spring are important for extratropical tropical interactions this paper focuses on one feature of these westerly ducts that has received relatively little attention to date the occurrence of rossby wave breaking events that transport tongues of extratropical air deep into the tropics mix tropical and subtropical air and can affect deep convection a climatology of these intrusion events formed from 20 years of meteorological analyses shows a strong dependence on the basic state flow notably intrusion events are found to occur almost exclusively within westerly ducts with more events in the presence of stronger equatorial westerlies it is also found that there is strong interannual variability in the frequency of pacific events with fewer events during the warm phases of enso consistent with the changes in the basic flow since these intrusion events laterally mix trace constituents and have been linked to tropical convection their spatial and temporal variability may cause related variability in the distribution of trace constituents and tropical convection

large geomagnetic field anomalies revealed in bronze to iron age archeomagnetic data from tel megiddo and tel hazor israel abstract geomagnetic field measurements from the past few centuries show heightened secular variation activity in the southern hemisphere associated with the south atlantic anomaly saa it is uncertain whether geomagnetic anomalies at a similar scale have existed in the past owing to limited coverage and uncertainties in the paleomagnetic database here we provide new evidence from archaeological sources in the levant suggesting a large positive northern hemisphere anomaly similar in magnitude to the saa during the 9th 8th centuries bce called levantine iron age anomaly we also report an additional geomagnetic spike in the 8th century the new dataset comprises 73 high precision paleointensity estimates from ca 3000 bce to 732 bce and five directional measurements between the 14th and the 9th centuries bce well dated pottery and cooking ovens were collected from twenty archaeological strata in two large contemporaneous stratigraphical mounds tells in israel tel megiddo and tel hazor the new data are combined with previously published data and interpreted automatically using the pmagpy thellier gui program the tel megiddo and tel hazor data sets demonstrate excellent internal consistency and remarkable agreement with published data from mesopotamia syria the data illustrate the evolution of an extreme geomagnetic high that culminated in at least two spikes between the 11th and the 8th centuries bce iron age in the levant the paleomagnetic directional data of the 9th century bce show positive inclination anomalies and deviations of up to 22 from the averaged geocentric axial dipole gad direction from comparison of the levantine archaeomagnetic data with igrf model for 2015 we infer the levantine iron age anomaly between the 10th and the 8th centuries bce is a local positive anomaly the eastward extent of the anomaly is currently unknown

site response for urban los angeles using aftershocks of the northridge earthquake ground motion records from aftershocks of the 1994 northridge earthquake are used to estimate site response in the urban los angeles area over 1300 shear wave records from 61 sources and 90 sites are used in a linear inversion for source and site response spectra the methodology makes no assumptions about the shape of the source spectrum to obtain a stable unique inverse a q model and geometrical spreading factor are assumed in addition the site response at a hard rock site is constrained to be approximately 1 0 with a kappa of 0 02 the site response spectra compare favorably with the results of previous and on going investigations in los angeles a couple of first order effects are lower site response in the surrounding mountains dominated by mesozoic and tertiary rocks and higher values in the san fernando and los angeles basins containing surficial pleistocene and holocene alluvial deposits results show good correlation of high site response spectral values with localized areas of severe damage interstate 10 collapse sherman oaks northridge interstate 5 14 collapse however widespread trends in site response across the sedimentary basins are not obvious the data suggest that site responses are lower near the southern margin of the san fernando valley for sources to the north due to north dipping sedimentary structures but the general pattern of site response is characterized by high variability on length scales less than a kilometer variations of a factor of 2 in site response are observed over the length scale of 200 m and for the same surficial geologic unit for some of the alluvial basin sites surface wave generation is a significant contributor to elevated site response at lower frequencies below 2 hz the total damage pattern for the northridge earthquake is influenced by strong source directivity to the north and strong local site effects the correlation of weak motion site response estimates with areas of significant damage demonstrates the value of these field measurements in future urban planning and in the reduction of seismic risk in urban areas

application of copper slag in geomagnetic archaeointensity research 1 paleointensity and archaeointensity studies since the 1950s have produced numerous geomagnetic intensity data for the last seven millennia as a consequence of different experiments and materials there is a complex and internally inconsistent picture of the geomagnetic field behavior in this study we present data using a recently developed experimental design on a heretofore unexploited recording medium copper slag deposits our results based on hundreds of specimens from various archaeometallurgical sites of the southern levant demonstrate the applicability of copper slag material for archaeointensity studies in addition to frequently exhibiting good experimental behavior slag has further advantages such as dense multilayer deposits and in cases embedded charcoals which open the door to data sets with excellent age control and resolution the data presented here augment the high quality database from the middle east and support previously observed periods of rapid change of the intensity of the geomagnetic field

magnetization of the la palma seamount series implications for seamount paleopoles paleopoles determined from seamount magnetic anomalies constitute the major data source for the pacific apparent polar wander path but relatively little is known about the processes of remanence acquisition in seamounts since magnetic anomalies reflect both natural remanence nrm and the induced field it is important first to assess whether the nrm is likely to represent an original field direction and second to constrain the magnitude of the induced component to this end we present paleomagnetic data from an uplifted subaerially exposed section through a seamount on la palma canary islands the pliocene seamount series of la palma comprises a 6 km sequence of alkalic extrusives and intrusives which includes all lithologies likely to be volumetrically important in seamounts the structural tilt of the seamount series allows separation of early thermal or chemical remanence from magnetization components acquired after tilting e g viscous remanence the nrm provides a poor indication of the original magnetization direction although the characteristic magnetization of many la palma samples is compatible with the original pretilt direction hydrothermal alteration has resulted in the production of ti poor magnetite and an increasing contribution of hematite with increasing degree of alteration more importantly well defined magnetization directions which deviate from any reasonable geomagnetic direction at la palma can be attributed to hydrothermal alteration in a different polarity than prevalent during the original magnetization based on a comparison of the magnitude of low stability components of magnetization and laboratory acquisition of viscous remanence and previous estimates of the induced magnetization we conclude that viscous and induced magnetization probably account for 15 25 of the total magnetization of seamounts the resulting paleopole bias is a function of the polarity and paleolatitude of the seamount and ranges from 4o to 16 o for cretaceous seamounts in the pacific

archaeomagnetic study of five mounds from upper mesopotamia between 2500 and 700 bce further evidence for an extremely strong geomagnetic field ca 3000 years ago the distribution of archaeomagnetic data in eastern europe and the near and middle east shows a remarkable gap in turkey this study presents the first archaeomagnetic results from five different mounds in southeast turkey the northern part of mesopotamia the rock magnetic experiments indicate that in the majority of the samples the dominant magnetic carrier is magnetite which is stable to heating to temperatures of 700 1c in general the demagnetization diagrams are single component and all five sets display well defined characteristic magnetizations and clustered directions for the period between 2500 and 700 bce the declinations are between 3501 and 201 while inclinations are in the range of 49 641 the directional results are compared with the global geomagnetic field models cals7k 2 arch3k cst 1 and cals3k 4 and the data from the archaeomagnetic database geomagia50v2 the results are coherent with both the data and the models except for two nearcontemporaneous sets dating 2000 bce which are offset to the east by more than 201 with respect to cals7k 2 archaeointensity measurements were made using the microwave and conventional thermal thellier methods applied to five sets of samples four furnaces and a mud brick wall these yielded comparable and intriguing results while those from the furnaces are slightly higher than the cals7k 2 model and in agreement with the geomagia50v2 and the middle east data the results from the mud brick wall suggest a high intensity of 100 8 mt 17 7 10 22 am 2 a t 1000 bce this result is

extreme geomagnetic field variability indicated by eastern mediterranean full vector archaeomagnetic records the magnetic field of the earth can exhibit considerable variations at short time scales even as short as decades the archaeomagnetic studies of middle eastern artefacts mainly from israel and jordan show evidence for an exceptionally high intensity period from 1050 700 bc which displays two distinct spikes over the levant the levantine iron age anomaly liaa its exact duration and geographical extent are still poorly known despite the wealth of ancient settlements the extensive cultural heritage and a long history of trade and immigration the archaeomagnetism of turkey and cyprus remains largely unexplored this study presents a large data set of ancient directions and intensities from seven archaeological sites in the eastern mediterranean covering a time span of 2000 yrs the recorded directions from thirteen sets of samples are coherent with our earlier findings yet show significantly larger swings than existing field models in particular we confirm the very large swing in inclination we found earlier from 1910 1850 bc that is also captured by the greek psv curve and shallower by more than 10 than predicted by existing field models consequently these models require substantial revision in this region we were able to determine the archaeointensity from five sets of mud bricks from the thirteen attempted allowing us to provide the full field vector furthermore we present thirty one new archaeointensity results from potsherds and mud bricks that considerably enhance existing data especially when a set of strict selection criteria is applied fourteen sets of potsherds from a single site tell atchana provide the longest sequence recorded so far in turkey from 2100 to 1350 bc we find exceptionally high intensities of 145 and 175 zam2 around 700 bc in well dated mud bricks and potsherds from two different locations tell tayinat and kilise tepe supporting extreme geomagnetic field variability in the region moreover these two high intensities confirm the younger spike of the liaa in turkey

possible impact of the earth s magnetic field on the history of ancient civilizations we report new archeointensity results from iranian and syrian archeological excavations dated from the second millennium bc these high temperature magnetization data were obtained using a laboratory built triaxial vibrating sample magnetometer together with our previously published archeointensity results from mesopotamia we constructed a rather detailed geomagnetic field intensity variation curve for this region from 3000 bc to 0 bc four potential geomagnetic events archeomagnetic jerks marked by strong intensity increases are observed and appear to be synchronous with cooling episodes in the north atlantic this temporal coincidence strengthens the recent suggestion that the geomagnetic field influences climate change over multi decadal time scales possibly through the modulation of cosmic ray flux interacting with the atmosphere moreover the cooling periods in the north atlantic coincide with episodes of enhanced aridity in the middle east when abrupt societal changes occurred in the eastern mediterranean and mesopotamia although the coincidences discussed in this paper must be considered with caution they lead to the possibility that the geomagnetic field impacted the history of ancient civilizations through climatically driven environmental changes triggering economic social and political instability

the study of earth s magnetism 1269 1950 a foundation by peregrinus and subsequent development of geomagnetism and paleomagnetism 1 this paper summarizes the histories of geomagnetism and paleomagnetism 1269 1950 the role of peregrinus is emphasized in the sixteenth century a debate on local versus global departures of the field from that of an axial dipole pitted gilbert against le nautonier regular measurements were undertaken in the seventeenth century at the turn of the nineteenth century de lamanon de rossel and von humboldt discovered the decrease of intensity as one approaches the equator around 1850 three figures of rock magnetism were fournet remanent and induced magnetizations delesse remagnetization in a direction opposite to the original and melloni direction of lava magnetization acquired at time of cooling around 1900 brunhes discovered magnetic reversals in the 1920s chevallier produced the first magnetostratigraphy and hypothesized that poles had undergone enormous displacements matuyama showed that the earth s field had reversed before the pleistocene our review ends in the 1940s when exponential development of geomagnetism and paleomagnetism starts

detecting multidomain magnetic grains in thellier palaeointensity experiments the thellier technique is the most commonly used method for absolute palaeointensity studies it is based on thellier s laws stating that partial thermoremanent magnetisations ptrms are independent and additive which however only are true for non interacting single domain sd grains for multidomain md grains individual ptrms are not independent and thellier palaeointensity experiments on rocks with a significant proportion of md grains may therefore lead to erroneous palaeofield estimates by introducing a ptrm tail check in the coe version of the thellier technique j geophys res 72 1967 3247 we present a simple method to detect and discard such rocks the usefulness of the ptrm tail check is exemplified by thellier palaeointensity experiments performed on two palaeomagnetic sample collections with different magnetomineralogy miocene baked sediments from french massif central are shown to be ideal for thellier studies with the remanent magnetisation residing in thermally stable sd grains for palaeocene eocene basaltic lavas from faeroe islands 64 of otherwise acceptable palaeointensity estimates are discarded due to the failure of ptrm tail checks indicating the presence of significant concentrations of md grains 2001 elsevier science b v all rights reserved

importance of cooling rate dependence of thermoremanence in paleointensity determination 1 the practical effect of cooling rate on the magnitude of thermal remanent magnetization trm is experimentally tested using both natural and synthetic magnetites for synthetic and natural single domain sd magnetites trm intensity increases as the cooling rate decreases because a longer exposure time for slower cooling offers more chances to achieve an equilibrium magnetization multidomain md magnetites have the opposite response trm decreases as the cooling rate increases because slower cooling allows more time to achieve lower magnetization because of self demagnetization for pseudo single domain psd magnetite the effect of cooling rate on the remanence intensity appears to be insignificant intermediate in behavior between sd and md for a sd trm differences are restricted to lower temperatures but diminish near the curie point strongly indicating a serious problem in a conventional treatment of cooling rate correction on the practical side merely applying trm differences as a correction can overcorrect the true paleointensity another important significance of the present study is that a cooling rate difference alone can cause a slight nonlinearity in an arai plot for a sd

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

summary of the gk15 ground motion prediction equation for horizontal pga and 5 damped psa from shallow crustal continental earthquakes we present a revised ground motion prediction equation gmpe for computing medians and standard deviations of peak ground acceleration pga and 5 damped pseudospectral acceleration psa response ordinates of the horizontal component of randomly oriented ground motions to be used for seismic hazard analyses and engineering applications this gmpe is derived from the expanded next generation attenuation nga west 1 database see data and resources 1 chiou et al 2008 the revised model includes an anelastic attenuation term as a function of quality factor q to capture regional differences in far source beyond 150 km attenuation and a new frequency dependent sedimentary basin scaling term as a function of depth to the 1 5 km s shear wave velocity isosurface to improve ground motion predictions at sites located on deep sedimentary basins the new graizer kalkan 2015 gk15 model developed to be simple is applicable for the western united states and other similar shallow crustal continental regions in active tectonic environments for earthquakes with moment magnitudes m 5 0 8 0 distances 0 250 km average shear wave velocities in the upper 30 m v s 30 200 1300 m s and spectral periods t 0 01 5 s our aleatory variability model captures interevent between event variability which decreases with magnitude and increases with distance the mixed effect residuals analysis reveals that the gk15 has no trend with respect to the independent predictor parameters compared to our 2007 2009 gmpe the pga values are very similar whereas spectral ordinates predicted are larger at t 0 2 s and they are smaller at longer periods 1 sec 21

the secular variation of the geomagnetic field in egypt in the last 5000 years the palaeo intensities fa of the geomagnetic field in egypt at some ages are determined by archaeomagnetic measurements and found to be fa 36 2 t at 3100 b c fa 46 8 t at 3000 b c fa 36 5 t at 2780 b c 49 0 t at 2500 b c 36 4 t at 2200 b c 57 5 t at 1990 b c 62 1 t atca 1400 b c 61 5 t at 1400 b c 69 9 t at 600 b c 59 3 t at 550 b c 79 9 t at 460 b c 73 7 t at 450 b c 69 7 t at 320 b c 56 2 t at a d 50 64 9 t at a d 400 54 4 t at a d 300 57 5 t at a d 700 and 43 0 t at a d 1975

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

high temperature archeointensity measurements from mesopotamia we present new archeointensity results obtained from 127 potsherds and baked brick fragments dated from the last four millennia bc which were collected from different syrian archeological excavations high temperature magnetization measurements were carried out using a laboratory built triaxial vibrating sample magnetometer triaxe and ancient field intensity determinations were derived from the experimental procedure described by le goff and gallet le goff and gallet earth planet sci lett 229 2004 31 43 as some of the studied samples were previously analyzed using the classical thellier and thellier thellier and thellier ann geophys 15 1959 285 376 method revised by coe coe j geophys res 72 1967 3247 3262 a comparison of the results is made from the two methods the differences both at the fragment and site levels are mostly within 5 which strengthens the validity of the experimental procedure developed for the triaxe the new data help to better constrain the geomagnetic field intensity variations in mesopotamia during archeological times with the probable occurrence of an archeomagnetic jerk around 2800 2600 bc

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

directional topographic site response at tarzana observed in aftershocks of the 1994 northridge california earthquake implications for mainshock motions abstract the northridge earthquake caused 1 78 g acceleration in the east west direction at a site in tarzana california located about 6 km south of the mainshock epicenter the accelerograph was located atop a hill about 15 m high 500 m long and 130 m wide striking about n78 e during the aftershock sequence a temporary array of 21 three component geophones was deployed in six radial lines centered on the accelerograph with an average sensor spacing of 35 m station c00 was located about 2 m from the accelerograph we inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion we identified a 3 2 hz resonance that is a transverse oscillation of the hill a directional topographic effect the top base amplification ratio at 3 2 hz is about 4 5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill this resonance is seen most strongly within 50 m of c00 other resonant frequencies were also observed a strong lateral variation in attenuation probably associated with a fault caused substantially lower motion at frequencies above 6 hz at the east end of the hill there may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill causing particle motions not spectral ratios at the top of the hill to be rotated about 20 away from the direction transverse to the hill the resonant frequency but not the amplitude of our observed topographic resonance agrees well with theory even for such a low hill comparisons of our observations with theoretical results indicate that the 3d shape of the hill and its internal structure are important factors affecting its response the strong transverse resonance of the hill does not account for the large east west mainshock motions assuming linear soil response mainshock east west motions at the tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill probable variations in surficial shear wave velocity do not account for the observed differences among mainshock acceleration observed at tarzana and at two different sites within 2 km of tarzana

trinet strong motion data from the m 7 1 hector mine california earthquake of 16 october 1999 the m w 7 1 hector mine earthquake of october 16 1999 was recorded by more than 300 stations of trinet which is administered cooperatively by the california division of mines and geology s california strong motion instrumentation program cdmg csmip california institute of technology and the u s geological survey usgs the earthquake occurred in a remote part of the mojave desert approximately 190 km northeast of downtown los angeles and there were no strong motion stations close to the surface rupture the nearest station hector is about 27 km north of the epicenter it recorded a peak horizontal ground acceleration of 0 33g the two next closest stations amboy and joshua tree are to the east and south both at epicentral distances of about 50 km each recorded peak ground accelerations of about 0 2g the new digital instruments installed for the trinet project recorded a large set of reliable data at epicentral distances up to 275 km these data can significantly improve empirical peak ground motion attenuation relationships which are usually developed for distances only up to 100 km boore et al 1993 1997 because adequate data have not been available at greater distances hector mine peak ground motions demonstrate reasonable agreement with empirical attenuation relationships for acceleration in contrast higher than expected ground velocities and displacements were recorded at epicentral distances of about 150 to 220 km especially in the los angeles sedimentary basin where anomalously high amplitude displacements with periods of 6 to 7 sec were recorded in los angeles long beach and other areas these long period surface or basin generated waves can have significant effects on large structures the m w 7 3 landers earthquake of 1992 similarly produced strong long period waves in the basin the peak ground motions produced by the landers earthquake were on average 1 6 times higher than for the hector mine earthquake in the los angeles area ground motion data recorded by digital instruments were uniformly processed in the frequency band 0 067 to 46 hz 0 022 15 sec the processed data set includes records from 213 ground response stations in an effort to make strong motion data available quickly to the engineering and scientific communities important records from this event were made available by file transfer protocol ftp beginning the day of the earthquake

eight thousand years of geomagnetic field intensity variations in the eastern mediterranean 1 twenty new intensity determinations of the ancient geomagnetic field have been obtained from groups of potsherds and brick fragments from syria these artifacts archeologically well dated from 6000 b c to approximately a d 1200 have been analyzed using the thellier and thellier 1959 method as modified by coe 1967 intensity values have been corrected for the effects of anisotropy of thermal remanent magnetization and cooling rate our results indicate that field intensities were moderate in syria from 6000 b c to 3500 b c with values of 30 40 t there was a significant increase in intensity by a factor of 2 from 3500 b c to 700 b c which was interrupted by a moderate decrease between 2550 b c and 1750 b c during more recent periods our results show an intensity minimum approximately a d 200 and a maximum around the tenth century comparison with different data sets from the eastern mediterranean and central asia shows that geomagnetic field intensity variations were consistent at this large regional scale at least over the last 5 millennia

predictions of shear wave velocities in southern california using surface geology a new model of the average shear wave velocity in the uppermost 30 m has been generated by extrapolation of discrete velocity profiles using surface geology at several scales statistical methods have been applied to create a map that is no more complicated than is supported by the velocity data several geologic units with similar responses are grouped together the resulting map is simpler than previous ones and yet fits the observed velocity profiles better than earlier more complicated maps analysis within a geographic information system will permit updates and modification of the map as new velocity data are added

geomagnetic field intensity how high can it get how fast can it change constraints from iron age copper slag article the intensity of the geomagnetic field varies over different time scales yet constraints on the maximum intensity of the field as well as for its maximum rate of change are inadequate due to poor temporal resolution and large uncertainties in the geomagnetic record the purpose of this study is to place firm limits on these fundamental properties by constructing a high resolution archaeointensity record of the levant from the 11th century to the early 9th century bce a period over which the geomagnetic field reached its maximum intensity in eurasia over the past 50 000 years we investigate a 14 c dated sequence of ten layers of slag material which accumulated within an ancient industrial waste mound of an iron age copper smelting site in southern israel depositional stratigraphy constrains relative ages of samples analyzed for paleointensity and 14 c dates from different horizons of the mound constrain the age of the whole sequence the analysis yielded 35 paleointenisty data points with accuracy better than 94 and precision better than 6 covering a period of less than 350 years most probably 200 years we construct a new high resolution quasi continuous archaeointensity curve of the levant that displays two dramatic spikes in geomagnetic intensity each corresponding to virtual axial dipole moment vadm in excess of 200 zam 2