holocene glacial activity and climatic variations in the swiss alps reconstructing a continuous record from proglacial lake sediments cores recovered from proglacial lake silvaplana swiss alps were investigated to examine the influence of holocene glaciers on lacustrine sedimentation during times of glacial activity in the catchment the sedimentation in the lake is dominated by the input of silt and clay sized material delivered by glacial meltwaters the deposition of fine grained material and the formation of varves reflect the existence of glaciers in the catchment and can therefore be used for the reconstruction of glacial history sedimentation rates are up to nine times higher in the varved than in the non varved sediments indicating significantly higher erosion rates under glaciated catchment conditions glacial varves were deposited in lake silvaplana during glacial retreat in the latest pleistocene and early holocene until 9400bp non varved deposits having a higher organic content and coarser grain sizes accumulated at lower rates when glacial activity was absent or negligible within the catchment between 9400 and 3300 bp

a flexible approach to assessing synchroneity of past events using bayesian reconstructions of sedimentation history the dating of depths in two or more cores is frequently followed by a study of the synchroneity or otherwise of events reflected in the cores the difficulties most frequently encountered are a determining precisely the depths associated with the events and b determining the ages associated with the depths there has been much progress in recent years in developing tools for the study of uncertainties in establishing chronologies this has not yet been matched by similar progress in modelling event depth relationships this paper proposes a simple and flexible approach showing how uncertain events can be married to uncertain chronologies difficulties in studying event depth age relationships typically involve a confounding of two different problems first what exactly do we mean by an event a point in history a single depth in the core corresponding to a single time or a depth time range sometimes event is in fact a shorthand for a space time process do the data reflect more than one type of event process this can reflect vagueness in definition second what are the sources and implications of the uncertainties here we illustrate the issues involved by examination of several features seen in north european holocene pollen records the alnus rise is regarded as a diachronous early holocene event in contrast the ulmus decline is widely seen as a near synchronous event in the mid holocene the third feature we examine is the interval between the ulmus decline and the first occurrence of cerealia type pollen the evidence for these events lies in cores of lake sediment from which are determined a the proportions of pollen at many depths and b radiocarbon age estimates from usually fewer depths for this illustration we focus on six sites we draw attention to a new and flexible method implemented in the free r software package bchron haslett j parnell a 2008 a simple monotone process with application to radiocarbon dated depth chronologies journal of the royal statistical society series c 57 4 399 418 for the establishment of the uncertainties surrounding the dating of samples in such cores we illustrate its flexibility by assessing the synchroneity of past events

neoglaciation and an early little ice age in western norway lichenometric evidence from the sandane area moraine sequences protalus ramparts rock glaciers and various slope deposits in seven separate glacier basins provide lichenometric ages for glacier retreat in an upland area of sogn og fjordane southern norway geomorphological mapping relative dating based on section rhizocarpon size frequency distributions observations on vegetation cover and numeric dating based on a regional lichen dating curve for section rhizocarpon place moraines into three groups stage 1 moraines of likely preboreal or younger dryas age stage 2 moraines of pre or early little ice age but post preboreal age thirteenth fourteenth centuries and stage 3 moraines of fifteenth century age and younger the occurrence of thirteenth sixteenth century pre or early little ice age moraines at low altitudes in the sandane area is thought to relate to greater availability of moisture and to the capture of wind drifted snow these moraines are some of the oldest little ice age moraines dated by lichenometry in southern n

geochemical and statistical evaluation of groundwater in imphal and thoubal district of manipur india abstract in order to identify the hydrogeochemical process controlling the quality of groundwater an extensive study was carried out in imphal and thoubal district of manipur india the objectives of the studies were to delineate the spatial and temporal variability in groundwater quality and understand its suitability for human uses in the study area groundwater samples from 45 location have been collected during the pre monsoon monsoon and post monsoon seasons and analyzed for the major ions such as ca2 mg2 na k hco 3 cl so 4 2 no 3 po 4 3 f fe and silica the water quality of both districts was good for domestic and agricultural uses except for few samples these saline samples were localized and were due to the inherent lithology of the study area three major hydrochemical facies ca hco3 type mixed ca na hco3 and ca mg cl types in imphal district and ca hco3 mixed ca mg cl and ca cl type in thoubal district were identified the mineral stability diagrams indicated that the groundwater is in equilibrium with kaolinite and ca montmorillonite whereas gibbs plot showed that the chemical composition of ground water in both districts is controlled by the natural weathering processes irrespective of seasons among the chemical weathering processes silicate weathering was dominant the results were supported by wilcox plot and ussl diagrams the study reflected the overall suitability of groundwater for anthropogenic use

identification of hydrogeochemical zones in postglacial buried valley aquifer wielkopolska buried valley aquifer poland this article presents the difficulty in identifying the hydrochemical zoning of a semi confined aquifer characterised by a relative small spatial differentiation of groundwater chemistry it is shown that multivariate statistical methods can be used for the recognition and interpretation of the groundwater chemistry distribution in an aquifer the hydrochemical zonation caused by both natural and anthropogenic processes was identified using factor analyses in combination with a classical interpretation of the hydrogeological material the interpretation of the groundwater chemistry allows both identification of the aquifer recharge mechanism and verification of the groundwater flow system

the 8 2 ka event abrupt transition of the subpolar gyre toward a modern north atlantic circulation 1 climate model simulations of the 8 2 ka event show an abrupt strengthening of the atlantic subpolar gyre that allows us to connect two major but apparently contradictory climate events of the early holocene the freshwater outburst from proglacial lakes and the onset of labrador sea water formation the 8 2 ka event is the largest climatic signal of our present interglacial with a widespread cooling in the north atlantic region about 8200 years before present it coincides with a meltwater outburst from north american proglacial lakes that is believed to have weakened the atlantic meridional overturning circulation and northward heat transport followed by a recovery of the deep ocean circulation and rising temperatures after a few centuries marine proxy data however date the onset of deep water formation in labrador sea to the same time the subsequent strengthening of the slope current system created a regional signal recorded as an abrupt and persistent surface temperature decrease although similarities in timing are compelling a mechanism to reconcile these apparently contradictory events was missing our simulations show that an abrupt and persistent strengthening of the atlantic subpolar gyre provides a plausible explanation the intense freshwater pulse triggered a transition of the gyre circulation into a different mode of operation stabilized by internal feedbacks and persistent after the cessation of the perturbation as a direct consequence deep water formation around its center intensifies this corresponds to the modern flow regime and stabilizes the meridional overturning circulation possibly contributing to the holocene s climatic stability

strain rate and temperature dependence of omori law scaling constants of ae data implications for earthquake foreshock aftershock sequences 1 little is known about the temperature and strain rate dependence of acoustic emission ae activity ae hence we carried out a preliminary series of flow through triaxial compression tests on porous sandstones at different temperatures and strain rates the ae data exhibits clear foreshock and aftershock sequences with respect to the dynamic failure of the test specimen significant ae activity starts less than 5 min before sample failure irrespective of the strain rate the increase in the ae event rate is steeper and the foreshock exponent p is smaller in the slow strain rate tests it could be the reason why there are no easily recognisable foreshock sequences for most individual earthquakes the aftershock decay parameter p is a linear function of test temperature as it has also been inferred for natural seismicity the seismic b value decreases systematically with increasing deformation rate suggesting a greater proportion of small cracks in the slow strain rate tests hence the ae activity is a function of both strain rate and temperature

normalizing xrf scanner data a cautionary note on the interpretation of high resolution records from organic rich lakes x ray fluorescence xrf scanning of unlithified untreated sediment cores is becoming an increasingly common method used to obtain paleoproxy data from lake records xrf scanning is fast and delivers high resolution records of relative variations in the elemental composition of the sediment however lake sediments display extreme variations in their organic matter content which can vary from just a few percent to well over 50 as xrf scanners are largely insensitive to organic material in the sediment increasing levels of organic material effectively dilute those components that can be measured such as the lithogenic material the closed sum effect consequently in sediments with large variations in organic material the measured variations in an element will to a large extent mirror the changes in organic material it is therefore necessary to normalize the elements in the lithogenic component of the sediment against a conservative element to allow changes in the input of the elements to be addressed in this study we show that al which is the lightest element that can be measured using the itrax xrf scanner can be used to effectively normalize the elements of the lithogenic fraction of the sediment against variations in organic content we also show that care must be taken when choosing resolution and exposure time to ensure optimal output from the measurements

palaeo hydrogeological control on groundwater as levels in red river delta vietnam to study the geological control on groundwater as concentrations in red river delta depth specific groundwater sampling and geophysical logging in 11 monitoring wells was conducted along a 45 km transect across the southern and central part of the delta and the literature on the red river delta s quaternary geological development was reviewed the water samples n 30 were analyzed for as major ions fe 2 h 2 s nh 4 ch 4 18 and 8d and the geophysical log suite included natural gamma ray formation and fluid electrical conductivity the sw part of the transect intersects deposits of grey estuarine clays and deltaic sands in a 15 20 km wide and 50 60m deep holocene incised valley the ne part of the transect consists of 60 120 m of pleistocene yellowish alluvial deposits underneath 10 30m of estuarine clay overlain by a 10 20m veneer of holocene sediments the distribution of 18 o values range 12 2 to 6 3 o and hydraulic head in the sample wells indicate that the estuarine clay units divide the flow system into an upper holocene aquifer and a lower pleistocene aquifer the groundwater samples were all anoxic and contained fe 2 0 03 2 0mm mn 0 7 320 m so 4 2 1 m 0 75mm h 2 s 0 1 7 0 m nh 4 0 03 4 4 mm and ch 4 0 08 14 5 mm generally higher concentrations of nh 4 and ch 4 and low concentrations of so 4 were found in the sw part of the transect dominated by holocene deposits while the opposite was the case for the ne part of the transect the distribution of the groundwater as concentration 0 013 11 7 m median 0 12 m 9 g l is related to the distribution of nh 4 ch 4 and so 4 low concentrations of as 0 32 m were found in the pleistocene aquifer while the highest as concentrations were found in the holocene aquifer phre eqc 2 speciation calculations indicated that fe 2 and h 2 s concentrations are controlled by equilibrium for disordered mackinawite and precipitation of siderite an elevated groundwater salinity cl range 0 19 65 1 mm was observed in both aquifers and dominated in the deep aquifer a negative correlation between aqueous as and an estimate of reduced so 4 was observed indicating that fe sulphide precipitation poses a secondary control on the groundwater as concentration

earthquake monitoring in southern california for seventy seven years 1932 2008 the southern california seismic network scsn has produced the scsn earthquake catalog from 1932 to the present a period of more than 77 yrs this catalog consists of phase picks hypocenters and magnitudes we present the history of the scsn and the evolution of the catalog to facilitate user understanding of its limitations and strengths hypocenters and magnitudes have improved in quality with time as the number of stations has increased gradually from 7 to 400 and the data acquisition and measuring procedures have become more sophisticated the magnitude of completeness m c of the network has improved from m c 3 25 in the early years to m c 1 8 at present or better in the most densely instrumented areas mainshock aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470 000 events the earthquake frequency size distribution has an average b value of 1 0 with m 6 0 events occurring approximately every 3 yrs the three largest earthquakes recorded were 1952 m w 7 5 kern county 1992 m w 7 3 landers and 1999 m w 7 1 hector mine sequences and the three most damaging earthquakes were the 1933 m w 6 4 long beach 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes all of these events ruptured slow slipping faults located away from the main plate boundary fault the san andreas fault their aftershock sequences constitute about a third of the events in the catalog the fast slipping southern san andreas fault is relatively quiet at the microseismic level and has not had an m 6 earthquake since 1932 in contrast the slower san jacinto fault has the highest level of seismicity including several m 6 events thus the spatial and temporal seismicity patterns exhibit a complex relationship with the plate tectonic crustal deformation

exploring remote earthquake triggering potential across earthscopes transportable array through frequency domain array visualization to better understand earthquake source processes involved in dynamically triggering remote aftershocks we use data from the earthscope transportable array ta that provide uniform station sampling similar recording capabilities large spatial coverage and in many cases repeat sampling at each site to avoid spurious detections which are an inevitable part of automated time domain amplitude threshold detection methods we develop a frequency domain earthquake detection algorithm that identifies coherent signal patterns through array visualization this method is tractable for large data sets ensures robust catalogs and delivers higher resolution observations than what are available in current catalogs we explore seismicity rate changes local to the ta stations following 18 global main shocks m 7 that generate median peak dynamic stress amplitudes of 0 001 0 028 mpa across the array from these main shocks we find no evidence of prolific or widespread remote dynamic triggering in the continental u s within the main shock s wave train or following main shock stress transients within 2 days however limited evidence for rate increases exist in localized source regions these results suggest that for these data prolific remote earthquake triggering is a rare phenomenon throughout a wide range of observable magnitudes we further conclude that within the lower range of previously reported triggering thresholds surface wave amplitude does not correlate well with observed cases of dynamic triggering we propose that other characteristics of the triggering wavefield in addition to specific conditions at the site will drive the occurrence of triggering at these amplitudes

el nino variability off peru during the last 20 000 years here we present a high resolution marine sediment record from the el nino region off the coast of peru spanning the last 20 000 years sea surface temperature photosynthetic pigments and a lithic proxy for el nino flood events on the continent are used as paleo el nino southern oscillation proxy data the onset of stronger el nino activity in peru started around 17 000 calibrated years before the present which is later than modeling experiments show but contemporaneous with the heinrich event 1 maximum el nino activity occurred during the early and late holocene especially during the second and third millennium b p the recurrence period of very strong el nino events is 60 80 years el nino events were weak before and during the beginning of the younger dryas during the middle of the holocene and during medieval times the strength of el nino flood events during the last millennium has positive and negative relationships to global and northern hemisphere temperature reconstructions

bath s law derived from the gutenberg richter law and from aftershock properties 1 the empirical bath s law states that the average difference in magnitude between a mainshock and its largest aftershock is 1 2 regardless of the mainshock magnitude following vere jones 1969 and console et al 2003 we show that the origin of bath s law is to be found in the selection procedure used to define mainshocks and aftershocks rather than in any difference in the mechanisms controlling the magnitude of the mainshock and of the aftershocks we use the etas model of seismicity which provides a more realistic model of aftershocks based on i a universal gutenberg richter gr law for all earthquakes and on ii the increase of the number of aftershocks with the mainshock magnitude using numerical simulations of the etas model we show that this model is in good agreement with bath s law in a certain range of the model parameters

lacustrine evidence of holocene environmental change from three faroese lakes a multiproxy xrf and stable isotope study the vegetation history of the faroe islands has been investigated in numerous studies all broadly showing that the early holocene vegetation of the islands largely consisted of fellfield with gravely and rocky soils formed under a continental climate which shifted to an oceanic climate around 10 000 cal yr bp when grasses sedges and finally shrubs began to dominant the islands here we present data from three lake sediment cores and show a much more detailed history from geochemical and isotope data these data show that the faroe islands were deglaciated by the end of younger dryas 11 700 10 300 cal yr bp at this time relatively high sedimentation rates with high 13c imply poor soil development 13c ti and data reveal a much more stable and warm mid holocene until 7410 cal yr bp characterised by increasing vegetation cover and build up of organic soils towards the holocene thermal maximum around 7400 cal yr bp the final meltdown of the laurentide ice sheet around 7000 cal yr bp appears to have impacted both ocean and atmospheric circulation towards colder conditions on the faroe islands this is inferred by enhanced weathering and increased deposition of surplus sulphur sea spray and erosion in the highland lakes from about 7400 cal yr bp from 4190 cal yr bp further cooling is believed to have occurred as a consequence for increased soil erosion due to freeze thaw sequences related to oceanic and atmospheric variability this cooling trend appears to have advanced further from 3000 cal yr bp a short period around 1800 cal yr bp appears as a short warm and wet phase in between a general cooling characterised by significant soil erosion lasting until 725 cal yr bp interestingly increased soil erosion seems to have begun at 1360 cal yr bp thus significantly before the arrival of the first settlers on the faroe island around 1150 cal yr bp although additional erosion took place around 1200 cal yr bp possibly as a consequence of human activities hence it appears that if humans caused a change in the faroe landscape in terms of erosion they in fact accelerated a process that had already started soil erosion was a dominant landscape factor during the little ice age but climate related triggers can hardly be distinguished from human activities

aftershock detection thresholds as a function of time results from the anza seismic network following the 31 october 2001 ml 5 1 anza california earthquake we examine aftershock detectability thresholds for events in the initial part of the 31 october 2001 m l 5 1 sequence in southern california this sequence occurred directly below the broadband anza seismic network which recorded continuous waveform data at 13 azimuthally well distributed stations within the study region seven had epicentral distances 20 km of the 608 aftershocks 0 m l 2 8 in the initial 2 hr of this sequence the first five aftershocks recorded were only identifiable at stations within 30 km after applying a high pass filter using a cluster radius 1 1 km of 200 representative aftershocks we track the maximum seismogram amplitude versus earthquake magnitude this relationship helps us quantify the visibility of aftershocks within the mainshock coda and assess our detection capabilities we estimate that detectable aftershocks within the mainshock coda include 1 those over magnitude 3 that are within 15 km of the network centroid that occur 12 sec or more into the sequence and 2 those over magnitude 2 that are within 30 km of the centroid of the network that occur 60 sec or more into the sequence we find a lack of large aftershocks in this sequence the largest aftershock m l 2 8 is substantially smaller than the mainshock m l 5 1 we suggest this relatively large magnitude differential is dictated by a combination of factors that includes complexity of the san jacinto fault system and the lack of large earthquakes in the region in the past 20 years online material quicktime movies juxtaposing a 3 2 aftershock in the coda of a 5 1 mainshock

spectrocolorimetric interpretation of sedimentary dynamics the new q7 4 diagram colour is a fundamental property of sediment and is often used for lithographic description to determine sedimentological structures facies etc however the sedimentary information contained in this parameter is difficult to extract because it is difficult to quantify colour can be quantified by spectrocolorimetry which provides very high resolution data quickly and non destructively when adapted to sedimentology spectrocolorimeters prove to be powerful tools due to their low purchase and maintenance costs and some are portable and easily used in the field several methods have been used to extract sedimentological data from colorimetric spectra first derivatives factorial analysis etc in the present study we first provide a review of the sedimentological application of spectrophotometers and after having described these methods their advantages and disadvantages we then describe a new tool called the q7 4 diagram abscissa l ordinates 700 400 ratio this new technique permits sedimentological units to be defined allows the identification of different sediment components and provides 5 distinct poles clayey deposits organic rich deposits chlorophyll a and by products altered organic matter deposits iron rich deposits carbonated deposits coupled with the analysis of first derivative spectra it is possible to distinguish different pigments linked to the degradation and or nature of the organic material chlorophyll a melanoidin etc the state of iron oxidation for example hematite and goethite like signatures and the nature of clays the q7 4 diagram permits rapid acquisition of high resolution data on changes of sediment dynamics in geosystems that have been subjected to highly varied climatic environmental conditions the instrument is non destructive easy to use and maintain portable for use in the field fast to implement is capable of high resolution and has a vast range of possible applications spectrocolorimetry appears to provide many advantages and could become an essential and robust tool for preliminary sedimentological studies

reassessment of supposed early little ice age and older neoglacial moraines in the sandane area of western norway a reply to matthews nesje and dahl further evidence for an early little ice age in the sandane area southern norway is presented in support of the lichen data of evans et al 1994 and in response to the reassessment of matthews et al 1996 the geomorphological evidence for three phases of moraine deposition is clarified and relative age dating based upon schmidt hammer r values and soil development is presented these data in combination with the lichenometry reported earlier indicate that the moraines of the jardalen fagerdalen cirque in particular are not all of the same age pre little ice age as suggested by matthews et al 1996 but instead date either to post preboreal younger dryas times stage 1 moraines or to the little ice age stage 2 and 3 moraines the gradual increase in lichen diameters r values and soil depths from the youngest little ice age stage 3 moraine to the outermost and oldest stage 2 moraine lends further support to the suggestion that the little ice age in western nor way may have begun much earlier than previously documented in the literature problems in using the schmidt hammer for relative age dating in mountainous terrain where the moraines being dated are often con structed from old glacial deposits and fresh rock fall debris are also dis cussed

hydrogeochemical characteristics of groundwater from the two main aquifers in the red river delta vietnam abstract in the red river delta situated in the northern part of vietnam nearly its entire population depends solely on groundwater for daily water consumptions for this reason groundwater quality assessments must be carefully carried out using hydrogeochemical properties to ensure effective groundwater resource planning for the delta s present and future groundwater use in this study the spatial and seasonal changes in the hydrogeochemical characteristics of groundwater in the two main aquifers of the rrd were investigated by analyzing the physicochemical data obtained in 2011 from 31 conjunctive wells in the delta s holocene unconfined aquifer hua and pleistocene confined aquifer pca using the piper diagram and the gibbs diagram results of the data analysis show that the groundwater in both aquifers in the upstream area of the delta is dominated by the ca 2 hco 3 water type while the na cl dominates along the middle stream and downstream areas seasonal changes in the hydrogeochemical facies in both aquifers comparing the results for the dry and the rainy seasons were detected in about one third of the sampling wells which were mainly located at the upstream portion of the delta the hydrogeochemical facies of hua were different from that of pca by about 45 of the sampling wells in both the dry and the rainy seasons which were found mostly in the upstream and middle stream areas

seismicity rate immediately before and after main shock rupture from high frequency waveforms in japan 1 we analyze seismicity rate immediately before and after 82 main shocks with the magnitudes ranging from 3 to 5 using waveforms recorded by the hi net borehole array in japan by scrutinizing high frequency signals we detect 5 times as many aftershocks in the first 200 s as in the japan meteorological agency catalogue after correcting for the changing completeness level immediately after the main shock the aftershock rate shows a crossover from a slower decay with an omori s law exponent p 0 58 0 08 between 20 and 900 s after the main shock to a faster decay with p 0 92 0 04 after 900 s the foreshock seismicity rate follows an inverse omori s law with p 0 73 0 08 from several tens of days up to several hundred seconds before the main shock the seismicity rate in the 200 s immediately before the main shock appears steady with p 0 35 0 50 these observations can be explained by the epidemic type aftershock sequence etas model and the rate and state model for a heterogeneous stress field on the main shock rupture plane alternatively nonseismic stress changes near the source region such as episodic aseismic slip or pore fluid pressure fluctuations may be invoked to explain the observation of small p values immediately before and after the main shock

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

a strong correlation between induced peak dynamic coulomb stress change from the 1992 m7 3 landers california earthquake and the hypocenter of the 1999 m7 1 hector mine california earthquake the 1992 m7 3 landers earthquake may have played a role in triggering the 1999 m7 1 1 hector mine earthquake as suggested by their close spatial 20 km proximity current investigations of triggering by static stress changes produce differing conclusions when small variations in parameter values are employed here i test the hypothesis that large amplitude dynamic stress changes induced by the landers rupture acted to promote the hector mine earthquake i use a flat layer reflectivity method to model the landers earthquake displacement seismograms by requiring agreement between the model seismograms and data i can constrain the landers main shock parameters and velocity model a similar reflectivity method is used to compute the evolution of stress changes i find a strong positive correlation between the hector mine hypocenter and regions of large 4 mpa dynamic coulomb stress changes peak f t induced by the landers main shock a positive correlation is also found with large dynamic normal and shear stress changes uncertainties in peak f t 1 3 mpa are only 28 of the median value 4 6 mpa determined from an extensive set 160 of model parameters therefore the correlation with dynamic stresses is robust to a range of hector mine main shock parameters as well as to variations in the friction and skempton s coefficients used in the calculations these results imply dynamic stress changes may be an important part of earthquake trigging such that large amplitude stress changes alter the properties of an existing fault in a way that promotes fault failure

a case study of two m 5 mainshocks in anza california is the footprint of an aftershock sequence larger than we think it has been traditionally held that aftershocks occur within one to two fault lengths of the mainshock here we demonstrate that this perception has been shaped by the sensitivity of seismic networks the 31 october 2001 mw 5 0 and 12 june 2005 mw 5 2 anza mainshocks in southern california occurred in the middle of the densely instrumented anza seismic network and thus were unusually well recorded for the june 2005 event aftershocks as small as m 0 0 could be observed stretching for at least 50 km along the san jacinto fault even though the mainshock fault was only 4 5 km long it was hypothesized that an observed aseismic slipping patch produced a spatially extended aftershock triggering source presumably slowing the decay of aftershock density with distance and leading to a broader aftershock zone we find however the decay of aftershock density with distance for both anza se quences to be similar to that observed elsewhere in california this indicates there is no need for an additional triggering mechanism and suggests that given widespread dense instrumentation aftershock sequences would routinely have footprints much larger than currently expected despite the large 2005 aftershock zone we find that the probability that the 2005 anza mainshock triggered the m 4 9 yucaipa mainshock which occurred 4 2 days later and 72 km away to be only 14 1 this probability is a strong function of the time delay had the earthquakes been separated by only an hour the probability of triggering would have been 89 online material movies exploring the spatial extent of aftershocks from the 2001 and 2005 anza sequences

identification of spatio seasonal hydrogeochemical characteristics of the unconfined groundwater in the red river delta vietnam abstract groundwater has been the primary source of daily water supplies for people living in the red river delta the second largest delta in vietnam for this reason identification of hydrogeochemical properties of the groundwater is indispensable for sustainable utilization of groundwater sources in this study the spatio seasonal hydrogeochemical characteristics of groundwater in the unconfined aquifer of the red river delta have been investigated by systematically applying self organizing maps som and gibbs diagrams the groundwater chemistry dataset used in the analysis is composed of eight major dissolved ions i e ca2 mg2 na k hco 3 cl so 4 2 and co 3 2 and total dissolved solids that are collected from 47 groundwater monitoring wells within the study area during the dry and rainy seasons the som application classified the hydrogeochemical data into five clusters which revealed three basic representative water types high salinity one cluster low salinity two clusters and freshwater two clusters the spatial distribution of clusters and water types were identified in particular the low salinity type was found not only in the downstream area but also in the northeastern parts of the upstream and middle stream areas where the groundwater was mainly classified into one specific cluster in which agricultural activities were considered to influence groundwater chemistry cluster changes from the dry to rainy seasons were detected in approximately one fifth of the observations wells dilution by surface water may significantly affect the chemical characteristics of the unconfined aquifer during the rainy season based on gibbs diagrams rock weathering was found to be the main process in the evolution of chemical composition of freshwater type whereas the chemical structure of the low and high salinity types was primarily controlled by saltwater intrusion or anthropogenic activities

did the 2008 mw 7 9 wenchuan earthquake trigger the occurrence of the 2017 mw 6 5 jiuzhaigou earthquake in sichuan china

seismicity rate changes in the salton sea geothermal field and the san jacinto fault zone after the 2010 mw 7 2 el mayor cucapah earthquake

solute geochemistry and its sources of the groundwaters in the qinghai lake catchment nw china major ion compositions were analyzed in 65 groundwater samples to decipher water quality solute geochemistry and sources of groundwater within the qinghai lake catchment ne tibetan plateau groundwaters were slightly alkaline with ph varying from 7 2 to 8 7 the total dissolved solids tds varied over two orders of magnitude from fresh 88 to brackish 12 with a mean value of 672 mg l higher than river waters within the qinghai lake catchment and river waters draining the himalayas and the southeastern tibetan plateau most of the samples approximately 80 were the ca 2 mg 2 hco 3 type and suitable for drinking and irrigation some of the lakeside the buha and the qinghai lake water were cl type and not suitable for drinking and irrigation water quality of hargai and shaliu samples was better than the others rock weathering ion exchange and precipitation are the major geochemical processes responsible for the solutes in the groundwater within the qinghai lake catchment anthropogenic input to the groundwater is minor the forward models on the input of groundwaters from various sources showed that the contributions were 40 1 for carbonate weathering 29 0 for evaporite dissolution 16 8 for atmospheric input and 14 1 for silicate weathering of the total dissolved cations for the whole catchment evaporite dissolution was dominating in the lakeside the buha and the daotang samples contributing 15 3 45 9 20 4 61 1 and 21 3 63 9 of the total dissolved cations respectively carbonate weathering was dominated in the shaliu and the hargai samples contributing 23 9 71 7 and 31 8 95 4 of the total dissolved cations respectively the result also demonstrated that carbonate weathering had higher contribution to the groundwaters than silicate weathering

two terrestrial records of rapid climatic change during the glacial holocene transition 14 000 9 000 calendar years b p from europe two independent multidisciplinary studies of climatic change during the glacial holocene transition ca 14 000 9 000 calendar yr b p from norway and switzerland have assessed organism responses to the rapid climatic changes and made quantitative temperature reconstructions with modern calibration data sets transfer functions chronology at krakenes western norway was derived from calibration of a high resolution series of 14c dates chronologies at gerzensee and leysin switzerland were derived by comparison of 18o in lake carbonates with the 18o record from the greenland ice core project both studies demonstrate the sensitivity of terrestrial and aquatic organisms to rapid temperature changes and their value for quantitative reconstruction of the magnitudes and rates of the climatic changes the rates in these two terrestrial records are comparable to those in greenland ice cores but the actual temperatures inferred apply to the terrestrial environments of the two regions

hydrological and sedimentary controls leading to arsenic contamination of groundwater in the hanoi area vietnam the impact of iron arsenic ratios peat river bank deposits and excessive groundwater abstraction groundwater contamination by arsenic in vietnam poses a serious health threat to millions of people in the larger hanoi area elevated arsenic levels are present in both the holocene and pleistocene aquifers family based tubewells predominantly tap the holocene aquifer while the hanoi water works extract more than 600 000 m3 day of groundwater from the pleistocene aquifer detailed groundwater and sediment investigations were conducted at three locations exhibiting distinct geochemical conditions i e i high levels of dissolved arsenic av 121 g l at the river bank ii low levels of dissolved arsenic av 21 g l at the river bank and iii medium levels of dissolved arsenic 60 g l in an area of buried peat and excessive groundwater abstraction seasonal fluctuations in water chemistry were studied over a time span of 14 months sediment bound arsenic 1 3 22 g g is in a natural range arsenic correlates with iron r2 0 8 with variation related to grain size sediment leaching experiments showed that arsenic can readily be mobilized at each of the three locations low levels of arsenic in groundwater 10 g l generally exhibit manganese reducing conditions whereas elevated levels are caused by reductive dissolution under iron and sulphate reducing conditions average arsenic concentrations in groundwater are twofold higher at the river bank than in the peat area the lower levels of arsenic contamination in the peat area are likely controlled by the high abundance of iron present in both the aqueous and sediment phases with median molar fe as ratios of 350 in water and 8700 in the sediments of the peat area reduced iron possibly forms new mineral phases that resorb or sequester previously released arsenic to the sediment despite similar redox conditions resorption is much less significant at the river bank fe as aq 68 fe as s 4700 and hence arsenic concentrations in groundwater reach considerably higher levels drawdown of holocene water to the pleistocene aquifer in the peat area caused by the pumping for the hanoi water works clearly promotes reducing conditions in pleistocene groundwater this demonstrates that excessive abstraction of water from deep wells i e wells tapping water below the arsenic burdened depth can cause a downward shift of iron reducing conditions and concurrently mobilize arsenic along the way vertical migration of reduced groundwater may also impact aquifers under natural hydrological conditions seepage of doc enriched groundwater derived from degradation of organic matter in the clayey sediments at the river bank was observed to enhance and maintain iron reducing conditions in the aquifer where organic matter is scarce once the aquifer becomes reduced arsenic is released from the aquifer solid hosts but additionally derives from the arsenic enriched groundwater seeping from the clay into the aquifer this behaviour is an important mechanism for arsenic contamination in aquifers that might not necessarily contain enough organic matter in their sediments to induce reducing conditions independently

basic parameterization of schleswig holstein s shallow geological formations for numerical reactive transport simulations representative groundwater compositions groundwater protection has to remain ensured in spite of the ambition to apply more and various types of subsurface usages in future in this context numerical simulations using virtual aquifers can be suitable for evaluating the general effects of complex induced process interactions while meaningful simulation results require the appropriate parameterization of scenario analyses such as regarding representative groundwater compositions therefore this study reviewed the hydrochemical groundwater compositions of the different aquifers in the german state schleswig holstein to evaluate what aquifers exhibit statistically different compositions the nonparametric kruskal wallis test the analysis of variance the discriminant analysis and the hierarchical cluster analysis were applied these showed that between the free aquifers at ph 6 and the group of confined aquifers significant differences in the dissolved constituents exist but also that among the confined aquifers these differences are not significant except for saline groundwaters that can be present near underground salt structures and the north sea furthermore the two methods applied for deducting representative compositions were the nearest neighbor method where the monitoring wells accessing the groundwater most similar to the median compositions in the respective aquifers were identified and the cluster center analysis the calculated representative groundwater compositions for four aquifer groups acidic shallow aquifers neutral shallow aquifers confined freshwater aquifers saline aquifers using both methods were very similar thus this study provides a methodology and a basis for parameterizing virtual aquifer studies and discusses the limits of representativeness based on the regional data set

tornetrask tree ring width and density ad 500 2004 a test of climatic sensitivity and a new 1500 year reconstruction of north fennoscandian summers this paper presents updated tree ring width trw and maximum density mxd from tornetrask in northern sweden now covering the period ad 500 2004 by including data from relatively young trees for the most recent period a previously noted decline in recent mxd is eliminated non climatological growth trends in the data are removed using regional curve standardization rcs thus producing trw and mxd chronologies with preserved low frequency variability the chronologies are calibrated using local and regional instrumental climate records a bootstrapped response function analysis using regional climate data shows that tree growth is forced by april august temperatures and that the regression weights for mxd are much stronger than for trw the robustness of the reconstruction equation is verified by independent temperature data and shows that 63 64 of the instrumental inter annual variation is captured by the tree ring data this is a significant improvement compared to previously published reconstructions based on tree ring data from tornetrask a divergence phenomenon around ad 1800 expressed as an increase in trw that is not paralleled by temperature and mxd is most likely an effect of major changes in the density of the pine population at this northern tree line site the bias introduced by this trw phenomenon is assessed by producing a summer temperature reconstruction based on mxd exclusively the new data show generally higher temperature estimates than previous reconstructions based on tornetrask tree ring data the late twentieth century however is not exceptionally warm in the new record on decadal to centennial timescales periods around ad 750 1000 1400 and 1750 were equally warm or warmer the 200 year long warm period centered on ad 1000 was significantly warmer than the late twentieth century p 0 05 and is supported by other local and regional paleoclimate data the new tree ring evidence from tornetrask suggests that this medieval warm period in northern fennoscandia was much warmer than previously recognized

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

surface and deep ocean interactions during the cold climate event 8200 years ago evidence from a north atlantic deep sea sediment core reveals that the largest climatic perturbation in our present interglacial the 8200 year event is marked by two distinct cooling events in the subpolar north atlantic at 8490 and 8290 years ago an associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the atlantic meridional overturning circulation the existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying laurentide ice sheet margin

hydrochemical and isotopic patterns in a calc alkaline cu and au rich arid andean basin the elqui river watershed north central chile abstract the geochemistry of surface water and groundwater from the elqui river basin north central chile was studied in spring 2007 and fall 2008 to obtain a general understanding of the factors and mechanisms controlling the water chemistry of steep rivers located in mineral rich arid to semi arid zones besides its uniform intermediate igneous lithology this basin is known for acid drainage and high as contents in the el indio au cu as district in its andean head abundant tailings deposits are present in the middle part of the basin where agricultural activities are important according to the results the chemical and isotopic composition of the elqui basin surface water and groundwater is related to uniform calc alkaline lithology and the major polluting system of the chemically reactive but closed el indio mining district the resulting compositional imprints in surface and ground water are a high so4 levels reaching about 1000 mg l in the toro river water directly draining the mining area b a major depletion of fe and pollutant metals in surface water after the confluence of the toro and la laguna rivers c similar chemical composition of surface and ground waters that differ in h and o isotopic composition reflecting the effect of differential evaporation processes downstream of the puclaro dam and d seasonal variations of fe mn cu and zn in surface water in contrast the groundwater chemistry exhibits moderate seasonal changes mainly in hco 3 content in spite of the acid drainage pollution water quality is adequate for human consumption and irrigation this is a consequence of both the dominant calc alkaline lithology and the existing arid climate resulting in neutral to moderately alkaline ph values that are responsible for the precipitation of metal hydroxides and as sorption by fe oh 3

interpretation of undisturbed hydrogeochemical conditions in neogene sediments of the horonobe area hokkaido japan abstract empirical geostatistical and geochemical modeling techniques were used to determine whether chemical isotopic and mineralogical data collected in surface based borehole investigations at the horonobe underground research laboratory url site in hokkaido japan were representative of the natural environment before it was disturbed by borehole drilling hydraulic testing and sampling water samples collected either by pumping groundwaters to the surface from borehole sections that had been isolated by inflatable packers or by squeezing porewaters from drillcores sampled from the same borehole and sampling depth were found to be similar in certain respects m na m cl 18 o and d but not others m so42 m ca2 m mg2 and m k the inconsistencies suggest that a majority of the porewater samples were contaminated as a result of pyrite oxidation and dissolution of carbonate minerals during sampling storage and or squeezing of the drillcores multivariate geostatistical analyses support this hypothesis and further suggest that uncontaminated porewaters and groundwaters can be divided into three representative groups a low salinity low 18 o and low d group a moderate salinity low ca mg group and a high salinity high k and moderate ca mg group the groundwaters also contain high concentrations of dissolved gases including ch 4 g co 2 g h 2 s g and various hydrocarbons which exsolve from the groundwaters as they are pumped to the surface for sampling the effects of such degassing on the chemistry of groundwater samples was evaluated by using a reaction path model to simulate the titration of gases collected at the surface back into the samples results suggest that undisturbed groundwaters are slightly more acidic than their sampled counterparts and contain roughly equivalent activities of dissolved ch 4 aq and carbonate species redox potentials calculated using the corrected groundwater compositions and assuming equilibrium for the ch 4 aq co 2 aq redox couple are significantly more negative than those determined in situ in one borehole using a downhole chemical probe and those that can be inferred from the ubiquitous presence of small amounts of framboidal pyrite and siderite in siliceous biogenic sediments of the horonobe area the empirical geostatistical and geochemical modeling techniques considered in this study can be adapted for use in characterizing the hydrogeochemical environment of a site that will eventually be selected to host a geologic repository for high level nuclear waste in japan

detecting decadal changes in enso using neural networks the present manuscript analyzes monthly equatorial pacific indices by using a specific neural algorithm the so called self organizing maps soms the main result is a change found in the nature of the transitions between cold to warm and warm to cold extreme events from 1950 to present around the late 1970s som is an unsupervised clustering technique which allows one to reduce high dimensional data space in this case three indices over 636 months in terms of a smaller set of three dimensional reference vectors 100 characterizing pertinent situations these reference vectors which are displayed on a two dimension map are closely related by a topological relationship leading us to discriminate la nina conditions from the opposite el nino conditions in a second step a hierarchical agglomerative clustering hac method is used to further group the reference vectors into a small number of clusters 12 whose spatial and temporal characteristics can be analyzed and interpreted in terms of physical parameters schematically these 12 clusters can be divided into two warm clusters six neutral or transition clusters and four cold clusters in each particular group warm neutral cold the clusters mainly differ from each other by the amplitude of the anomalies their spatial patterns and their temporal variability some clusters are found to be strongly linked to the boreal spring period while others have barely any records during that season other clusters are associated with records mainly observed either prior to or after 1980 this suggests that the method is able to identify changes in the variability of the tropical pacific basin observed on decadal time scales 1976 climate shift in our case each monthly record can be summarized by the cluster to which it belongs the temporal evolution of this value during extreme enso events shows similar patterns persistence in specific clusters and transition between groups of clusters associated with comparable el nino or la nina events the methodology described in the present study som plus hac is suggested to be useful both for seasonal enso predictability and for the detection of decadal changes in enso behavior

a complete record of holocene glacier variability at austre okstindbreen northern norway an integrated approach arctic glaciers are currently undergoing major changes but accurate knowledge about how they varied during the entire holocene is still scarce here we present a new complete glacier record from austre okstindbreen in nordland northern norway this reconstruction is based on a number of short and long cores retrieved from several downstream basins which have been analyzed by a suite of methods including geochemical elements xrf rock magnetic properties dry bulk density dbd and loss on ignition loi lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar gpr independently lichen dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210pb dated lake sediment chronology this integrated approach reveals that austre okstindbreen is the first known glacier in scandinavia to possibly have survived the holocene thermal optimum it also brackets the four largest glacier advances to c 7400 7000 1400 1200 900 700 and 300 150 years before ad 2000 b2k in contrast to most reconstructed glaciers in scandinavia the largest glacier advance was not associated with the little ice age but rather to an earlier period centred at 1300 b2k both the moraine chronology and the lacustrine records document this neoglacial advance compared to other glacier reconstructions from the northern hemisphere we identify near synchronous glacier advances occurring roughly at 4000 b2k 2700 b2k 1300 b2k and during the little ice age these correlative advances across the northern hemisphere suggest that these observed centennial scale events are a shared feature regardless of the large geographical distances separating them some minor discrepancies between different geographical areas may be caused by lack of precise dating but local climatic conditions may play a role as well

evaluation of sedimentation vulnerability at small hillside reservoirs in the semi arid region of tunisia using the self organizing map small hillside reservoirs are fundamental for the sustainability of the water resources in the semi arid region of tunisia where the government has constructed small dams since 1990 however flash floods and severe erosion are jeopardizing the life of those small hydraulic structures prompting an assessment of the vulnerability of semi arid catchments to erosion in this study we investigated the degree of erosion in 23 catchments by considering six variables related to erosion the specific sediment yield the hypsometric integral the topographic index the rainfall related attribute as well as lithological and vegetation cover more importance was assigned to the hypsometric integral and how it controls erosion vulnerability the self organizing map of kohonen a robust clustering method was implemented to analyze the patterns of the six variables the results revealed four groups of catchments with different vulnerabilities to erosion in addition there is a global trend of increasing erosion risk from the southwest to the northeast of the semi arid region of tunisia

decay and expansion of the early aftershock activity following the 2011 mw9 0 tohoku earthquake the 2011 m w9 0 tohoku earthquake was followed by an abundant amount of seismicity providing a unique opportunity to analyze the triggering mechanism of great earthquakes although the tohoku earthquake occurred close to a dense seismic network many aftershocks that occurred in the first few hours after the mainshock are not recorded in the earthquake catalogs here we use a template waveform approach to recover as many as possible missing events in the first 12 hours following the tohoku mainshock our analysis is able to detect about 1 4 times more events than those listed in the high sensitivity seismograph hi net earthquake catalog combining our new dataset with earthquakes that occurred at latter times we are able to observe a continuous decay of the aftershock rate and along strike expansion of aftershock area we relate the latter observation to the occurrence of post seismic slip over the deep interface

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

a generalized omori s law for earthquake aftershock decay 1 earthquake aftershock sequences have been found to approximately satisfy three empirical scaling relations i the gutenberg richter frequency magnitude scaling ii bath s law for the difference in the magnitude of a mainshock and its largest aftershock and iii the modified omori s law for the temporal decay of aftershock rates the three laws are incorporated to give a generalized omori s law for aftershock decay rates that depend on several parameters specific for each given seismogenic region it is shown that the characteristic time c first introduced in the modified omori s law is no longer a constant but scales with a lower magnitude cutoff and a mainshock magnitude the generalized omori s law is tested against earthquake catalogs for the aftershock sequences of the landers northridge hector mine and san simeon earthquakes

omori utsu law c values associated with recent moderate earthquakes in japan we investigate the early aftershock activity associated with four moderate earthquakes m w 6 6 6 7 that occurred recently in japan for each aftershock sequence we examine continuous high pass filtered seismograms recorded at seismic stations nearby the main fault to identify as many early events as possible the magnitude of these events is calibrated using aftershocks that are listed in the earthquake catalog of japan meteorological agency jma the analysis of the aftershock decay rates reveals a power law time dependence with a scaling exponent close to 1 0 that starts from about one minute from the mainshock our results demonstrate that the c value of the omori utsu law is very small although a lower bound is not established due to completeness problems in the first minute after the mainshock and statistical fluctuations

a new approach to calculating holocene winter precipitation by combining glacier equilibrium line altitudes and pine tree limits a case stud from hardangerjokulen central southern norway at hardangerjokulen central southern norway detailed knowledge of the number age and magnitude of holocene glacier fluctuations is used to reconstruct variations in equilibrium line altitude ela for the last 10 000 years present and past elas are based on an accumulation area ratio aar of 0 7 and are adjusted for land uplift a synchronous relationship between advanced glacier positions and the highest pine tree limits pinus sylvestris l is demonstrated for the early to mid holocene in southern scandinavia which indicates that warm summers were compensated for by high winter precipitation based on pine tree limit fluctuations as a measure of mean ablation season temperature holocene variations in winter precipitation at hardangerjokulen have been calculated by substitution in the close exponential relationship between mean ablation season temperature and winter precipitation at the ela of norwegian glaciers setting the winter precipitation during the period ad 1961 1990 at 100 mean values

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

a new approach for reconstructing glacier variability based on lake sediments recording input from more than one glacier abstract we explore the possibility of building a continuous glacier reconstruction by analyzing the integrated sedimentary response of a large 440 km2 glacierized catchment in western norway as recorded in the downstream lake nerfloen n61 56 e6 52 a multi proxy numerical analysis demonstrates that it is possible to distinguish a glacier component in the 8000 yr long record based on distinct changes in grain size geochemistry and magnetic composition principal component analysis pca reveals a strong common signal in the 15 investigated sedimentary parameters with the first principal component explaining 77 of the total variability this signal is interpreted to reflect glacier activity in the upstream catchment an interpretation that is independently tested through a mineral magnetic provenance analysis of catchment samples minimum glacier input is indicated between 6700 5700 cal yr bp probably reflecting a situation when most glaciers in the catchment had melted away whereas the highest glacier activity is observed around 600 and 200 cal yr bp during the local neoglacial interval 4200 cal yr bp until present five individual periods of significantly reduced glacier extent are identified at 3400 3000 2700 2100 2000 1700 1500 and 900 cal yr bp

short term properties of earthquake catalogs and models of earthquake source i review the short term properties of earthquake catalogs in particular the time and size distributions and the completeness of the early part of aftershock sequences for strong shallow earthquakes i determine the parameters of the omori and gutenberg richter laws for aftershocks close in time to a mainshock aftershock sequences of large earthquakes in southern california 1952 kern county 1992 joshua tree landers big bear sequence 1994 northridge and 1999 hector mine recorded in the caltech catalog are analyzed to demonstrate that at the beginning of these series many small earthquakes are absent from the catalog the number of missing earthquakes increases with the magnitude range of a catalog and for some data sets exceeds the number of aftershocks close to a mainshock listed in a catalog comparing global earthquake catalogs harvard centroid moment tensor and preliminary determination of epicenter with local data sets indicates that the catalogs based on longer period waves miss many early aftershocks even when their magnitudes are well above the stated magnitude threshold such short term incompleteness may introduce significant biases to the statistical analysis of the seismicity pattern in particular for branching models of earthquake occurrence incorporating the omori law for such models the likelihood function strongly depends on close aftershocks i review the techniques to alleviate this problem analyzing the source rupture process of several recent large earthquakes suggests that rupture propagation is highly inhomogeneous in space time and focal mechanism these random variations in the rupture process can be viewed as an extension of the aftershock stochastic generating mechanism toward the origin time of a mainshock i review various models of the earthquake rupture process and suggest that fractal distributions of microevents in time space and focal mechanism constitute the development of an earthquake the final identification of an individual earthquake depends on both objective and subjective factors manuscript received 21 may 2003

numerical analyses of a multi proxy data set from a distal glacier fed lake sorsendalsvatn western norway abstract here we present a holocene record of glacier variability as documented through physical sediment properties analysed on sediments from the distal glacier fed lake nedre nedre lower sorsendalsvatn 918 m a s l located 35 km inland from the coast in western norway we emphasise comparing different sediment parameters by means of statistical methods as well as integrating chronological uncertainties along with uncertainties of reconstructed glacier variability a multi proxy data set consisting of sedimentological physical and geochemical data shows one main process as extracted by means of principal component analysis 88 of the variance explained by the first pc driving sediment variability in nedre sorsendalsvatn the common signal extracted from the sediment data is indicative of glacial activity in the catchment and is interpreted to vary in concert with the changing glacier equilibrium line altitude the reconstruction of former glacier activity is in accordance with glacier variability reconstructed from other sites in western norway including the termination of the deglaciation at approximately 10 000 cal yr bp the 8 2 ka bp finse event the holocene thermal optimum between 8000 and 5500 cal yr bp and the onset of the neoglacial at 5500 cal yr bp the largest glacial extent during the neoglacial time period took place during the little ice age the combined radiocarbon chronologies from three different sediment cores provide insight into the duration of the 8 2 ka event in the terrestrial system the maximum glacier activity at approximately 8 2 cal bp is the culmination of a glacier advance that began around 9 cal bp and accelerated at 8 4 cal bp the glacier advance ended abruptly at 8 0 cal bp

common dependence on stress for the two fundamental laws of statistical seismology the gutenberg richter relation and the omori utsu law both power laws are two of the long standing relationships of statistical seismology here aftershock sequences are described according to the faulting style of their main shocks showing that the time delay before the onset of the power law aftershock decay rate is on average shorter for thrust main shocks than for normal fault earthquakes these similar dependences on the faulting style indicate that both the fundamental power laws are governed by the state of stress

seismology dynamic triggering of earthquakes the landers earthquake of 1992 triggered a series of earthquakes in other parts of california focusing attention on the mechanism of remote triggering laboratory experiments on granular material under pressure suggest that triggering is a result of seismic waves impinging on a fault and inducing elastic nonlinear behaviour of the fault core accompanied by instantaneous weakening and failure the resulting softening to weakening model fits in well with field observations of real earthquakes after an earthquake numerous smaller shocks are triggered over distances comparable to the dimensions of the mainshock fault rupture although they are rare at larger distances here we analyse the scaling of dynamic deformations the stresses and strains associated with seismic waves with distance from and magnitude of their triggering earthquake and show that they can cause further earthquakes at any distance if their amplitude exceeds several microstrain regardless of their frequency content these triggering requirements are remarkably similar to those measured in the laboratory for inducing dynamic elastic nonlinear behaviour which suggests that the underlying physics is similar1 2

rapid earthquake characterization using mems accelerometers and volunteer hosts following the m 7 2 darfield new zealand earthquake we test the feasibility of rapidly detecting and characterizing earthquakes with the quake catcher network qcn that connects low cost microelectromechan ical systems accelerometers to a network of volunteer owned internet connected com puters following the 3 september 2010 m 7 2 darfield new zealand earthquake we installed over 180 qcn sensors in the christchurch region to record the aftershock se quence the sensors are monitored continuously by the host computer and send trigger reports to the central server the central server correlates incoming triggers to detect when an earthquake has occurred the location and magnitude are then rapidly esti mated from a minimal set of received ground motion parameters full seismic time series are typically not retrieved for tens of minutes or even hours after an event we benchmark the qcn real time detection performance against the gns science geonet earthquake catalog under normal network operations qcn detects and characterizes earthquakeswithin9 1softheearthquakeruptureanddeterminesthemagnitudewithin 1 magnitude unit of that reported in the gns catalog for 90 of the detections

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

hydro geochemical processes in an area with saline groundwater in lower shire river valley malawi an integrated application of hierarchical cluster and principal component analyses abstract our ability to adapt to changes in groundwater quality arising from a changing climate and or local pressures is dependent on comprehension of the governing controls of spatial variation in groundwater chemistry this paper presents results of an assessment of dominant hydro geochemical processes controlling groundwater chemical composition using an integrated application of hierarchical cluster analysis hca and principal component analysis pca of a major ion dataset of groundwater from lower shire river valley malawi the area is in the southernmost part of the western section of the east african rift system ears and has localised occurrence of saline groundwater hca classified samples into three main clusters c1 c3 according to their dominant chemical composition c1 dominant composition na cl median tds 3436 mg l 1 c2 dominant composition na hco 3 median tds 966 mg l 1 and c3 dominant composition alkali earths hco 3 median tds 528 mg l 1 these clusters were in turn described by the principal components pc1 pc3 and pc2 respectively resulting from the pca the results of the pca and geochemical interpretation suggest that the spatial variation of groundwater quality in the area is influenced by the following processes c3 samples result mainly from h 2 co 3 weathering of aluminosilicate minerals by percolating water supersaturated with co 2 in addition to aluminosilicate weathering c2 samples are influenced by the processes of cation exchange of ca 2 and mg 2 in the water for na on clay minerals and carbonate precipitation the increase in ionic strength of c2 samples is attributed to mixing with high tds groundwater in proximity with c2 samples the saline brackish c1 groundwater results from the processes of evaporation for samples with high water table close to the shire marshes and dissolution of cl and so 4 evaporative salts followed by mineralised seep from sedimentary karoo and cretaceous lupata sandstones

relocation of early and late aftershocks of the 2001 bhuj earthquake using joint hypocentral determination jhd technique implication toward the continued aftershock activity for more than four years we employed layered model joint hypocentral determination jhd with station corrections to improve location identification for the 26 january 2001 mw 7 7 bhuj early and late aftershock sequence we relocated 999 early aftershocks using the data from a close combined network national geophysical research institute india and center for earthquake research institute usa of 8 18 digital seismographs during 12 28 february 2001 additionally 350 late aftershocks were also relocated using the data from 4 10 digital seismographs accelerographs during august 2002 to december 2004 these precisely relocated aftershocks error in the epicentral location 30 meter error in the focal depth estimation 50 meter delineate an east west trending blind thrust north wagad fault nwf dipping 45 southward about 25 km north of kachchh main land fault kmf as the causative fault for the 2001 bhuj earthquake the aftershock zone is confined to a 60 km long and 40 km wide region lying between the kmf to the south and nwf to the north extending from 2 to 45 km depth estimated focal depths suggest that the aftershock zone became deeper with the passage of time the p and s wave station corrections determined from the jhd technique indicate that the larger values both ve and ve characterize the central aftershock zone which is surrounded by the zones of smaller values the station corrections vary from 0 9 to 1 1 sec for the p waves and from 0 7 to 1 4 sec for the s waves the b value and p value of the whole aftershock 2001 2004 sequences of mw 3 are estimated to be 0 77 0 02 and 0 99 0 02 respectively the p value indicates a smaller value than the global median of 1 1 suggesting a relatively slow decay of aftershocks whereas the relatively lower b value less than the average b value of 1 0 for stable continental region earthquakes of india suggests a relatively higher probability for larger earthquakes in kachchh in comparison to other stable continental regions of the indian peninsula further based on the b value mainshock magnitude and maximum aftershock magnitude the bhuj aftershock sequence is categorized as the mogi s type ii sequence indicating the region to be of intermediate level of stresses and heterogeneous rocks it is inferred that the decrease in p value and increase in aftershock zone both spatially as well as depth over the passage of time suggests that the decay of aftershocks perhaps could be controlled by visco elastic creep in the lower crust

holocene and latest pleistocene climate and glacier fluctuations in iceland abstract multiproxy climate records from iceland document complex changes in terrestrial climate and glacier fluctuations through the holocene revealing some coherent patterns of change as well as significant spatial variability most studies on the last glacial maximum and subsequent deglaciation reveal a dynamic iceland ice sheet iis that responded abruptly to changes in ocean currents and sea level the iis broke up catastrophically around 15 ka as the polar front migrated northward and sea level rose indications of regional advance or halt of the glaciers are seen in late allerod early younger dryas time and again in preboreal time due to the apparent rise of relative sea level in iceland during this time most sites contain evidence for fluctuating tidewater glacier termini occupying paleo fjords and bays the time between the end of the younger dryas and the preboreal was characterized by repeated jokulhlaups that eroded glacial deposits by 10 3 ka the main ice sheet was in rapid retreat across the highlands of iceland the holocene thermal maximum htm was reached after 8 ka with land temperatures estimated to be 3 c higher than the 1961 1990 reference and net precipitation similar to modern such temperatures imply largely ice free conditions across iceland in the early to mid holocene several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8 5 and 8 ka but no moraines have been detected from that time termination of the htm and onset of neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4 5 and 4 0 ka intensifying between 3 0 and 2 5 ka although a distinct warming during the medieval warm period is not dramatically apparent in icelandic records the interval from ca ad 0 to 1200 is commonly characterized by relative stability with slow rates of change the literature most commonly describes little ice age moraines ca ad 1250 1900 as representing the most extensive ice margins since early holocene deglaciation with temperature depressions of 1 2 c compared to the ad 1961 1990 average steep north south and west east temperature gradients are reconstructed in the holocene records of iceland suggesting a strong maritime influence on the terrestrial climate of iceland

hydrochemical evolution of the east midlands triassic sandstone aquifer england a detailed hydrogeochemical interpretation has been made of the red bed sherwood sandstone triassic aquifer of the east midlands of england on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water three distinct zones are recognised 1 i recent groundwater mainly 100 y oxidising dominated by congruent dissolution of dolomite and by inputs from atmospheric and anthropogenic sources 2 ii groundwater age 103 104 y predominantly reducing dominated by incongruent dissolution of dolomite 3 iii groundwater age 104 y reducing conditions approach to isotopic and chemical equilibrium in the carbonate system dominance of gypsum dissolution the minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history na cl f and b are controlled by atmospheric inputs sr2 and mn2 trends can be explained by carbonate and sulphate mineral dissolution ba2 is derived from carbonates but controlled by barite equilibrium fe so42 no3 and u are strongly influenced by redox reactions the concentrations of transition metals and other elements remain very low only li and k are considered to represent additions by reaction of silicate minerals the extent of direct anthropogenic influence is probably limited to enhanced so4 no32 and possibly cu zn and pb in zone i

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

scaling properties of the parkfield aftershock sequence aftershock sequences present a unique opportunity to study the physics of earthquakes important questions concern the fundamental origin of three widely applicable scaling laws 1 gutenberg richter frequency magnitude scaling 2 omori s law for aftershock decay rates and 3 bath s law for the difference between the magnitude of the largest aftershock and a mainshock the high resolution parkfield seismic network provided the opportunity for detailed studies of the aftershock sequence following the 28 september 2004 m 6 0 parkfield earthquake in this article it is shown that aftershocks satisfy the gutenberg richter scaling relation only for relatively large times after the mainshock there is a systematic time delay for the establishment of this scaling law the temporal evolution of the rates of occurrence of aftershocks is quantified using the generalized omori s law this scaling law contains two characteristic times c and the analysis suggests that the parameter c plays the role of a characteristic time for the establishment of gutenberg richter scaling this time increases systematically with a decreasing lower magnitude cutoff the systematic time delay is attributed to a cascade of energy from long wavelengths to short wavelengths the parameter is a measure of the average time until the first aftershock occurs we find that slightly varies with the lower magnitude cutoff of the sequence we also note that the largest aftershock inferred from an extrapolation of gutenberg richter scaling m 5 0 is equal to the largest observed aftershock this scaling associated with the universal applicability of bath s law is attributed to a constant partitioning of energy between a mainshock and its associated aftershock sequence we also give in this article the distribution of interoccurrence times between successive aftershocks we show that this distribution is well approximated by a nonhomogeneous poissons process driven by the modified omori s law the self consistency between interoccurrence statistics and decay rates is taken as further evidence for the applicability of our studies

delineation of hydrochemical facies distribution in a regional groundwater system by means of fuzzy c means clustering 1 in this paper classification of a large hydrochemical data set more than 600 water samples and 11 hydrochemical variables from southeastern california by fuzzy c means fcm and hierarchical cluster analysis hca clustering techniques is performed and its application to hydrochemical facies delineation is discussed results from both fcm and hca clustering produced cluster centers prototypes that can be used to identify the physical and chemical processes creating the variations in the water chemistries there are several advantages to fcm and it is concluded that fcm as an exploratory data analysis technique is potentially useful in establishing hydrochemical facies distribution and may provide a better tool than hca for clustering large data sets when overlapping or continuous clusters exist index terms 1806 hydrology chemistry of fresh water 1829 hydrology groundwater hydrology 1831 hydrology groundwater quality 1871 hydrology surface water quality keywords clustering techniques fuzzy logic fuzzy c means hydrochemical facies hydrochemistry inverse modeling

reassessment of supposed early little ice age and older neoglacial moraines in the sandane area of western norway neoglacial moraines that are substantially older than the conventional little ice age glacier maximum of the mid eighteenth century have been recognized recently in the sandane area of western norway this is important in the context of scandinavian holocene glacier variations because in southern scandinavia at least it is widely accepted that glaciers were larger in the mid eighteenth century than at any time since the preboreal in this report we question and test the age of supposed early little ice age and older neoglacial moraines in two valleys in the sandane area observations and data relating to moraine morphology licheno metry and vegetation cover are reassessed and new lines of evidence based on boulder weathering schmidt hammer soil development and glaciofluvial activity are introduced critical appraisal of the evidence leads to the conclusion that the existence of pre or early little ice age moraines dating from the thirteenth to seventeenth centuries or indeed older neoglac

seismicity in the western great basin apparently triggered by the landers california earthquake 28 june 1992 within 24 hr after the landers earthquake there were three magnitude 3 4 events in western nevada and an unexpected widespread increase in the rate of small events based on combined catalogs for northern nevada southern nevada and southern california and a model that assumes statistical independence of events in these regions the probability of this happening in a 24 hr period by random chance is less than 10 12 per day therefore there is high statistical confidence that the increased seismicity was triggered by the landers event based on the statistical model we develop a list of 227 earthquakes in the first 83 days following the landers earthquake each of which has no more than 10 probability of occurring by random chance the suspect events are broadly distributed in regions that correlate with historical activity in the great basin the events are not uniquely associated with known volcanic activity or with zones that were previously active with microearthquakes or aftershock sequences the magnitudes of the largest triggered events appear to decrease with distance with time the number of suspect events decreases at a rate comparable to the rate of decrease of aftershocks of the landers and big bear earthquakes three of the most significant triggered events that that occurred were as follows mina 500 km from landers m 4 36 min after landers smith valley 590 km from landers m 3 4 56 min after landers and little skull mountain 280 km from landers m 5 6 22 3 hr after landers the evidence for triggering is particularly strong in the case of the little skull mountain event where an increased rate of microseismicity was evident as soon as small events could be identified in the coda of the landers earthquake we evaluate the seismic history for the past 3 yr to understand what was unique about the landers earthquake this includes identifying the previous earthquakes most likely to have caused the strongest shaking in various frequency bands based on a simple screening model the strains from the landers earthquake were uniquely large at low frequencies but at high frequencies they were exceeded frequently by small more local events thus we hypothesize that the cause of triggering is low frequency dynamic strains at periods of about 10 sec or greater and that there is a regional threshold that must be exceeded since previous events with calculated strains that were almost as strong were not causes of widespread triggering this mechanism for triggering satisfies the criterion of being a relatively rare phenomenon since it is likely to occur only when a large long period wave is radiated into an area where strain has been building slowly toward the point where faults are unstable

utilizing physical sediment variability in glacier fed lakes for continuous glacier reconstructions during the holocene northern folgefonna western norway the maritime plateau glacier of northern folgefonna in western norway has a short subdecadal response time to climatic shifts and is therefore well suited for reconstructing high resolution glac

in situ reflectance spectroscopy analysing techniques for high resolution pigment logging in sediment cores the temporal resolution of marine proxy data is limited by analytically required sample size we present in situ reflectance spectroscopy techniques usually applied in remote sensing to analyse the organic fraction of marine and terrestrial sediment from absorption band depths photosynthesis pigment variations are derived for sediments from the upwelling region off peru where productivity is related to the annual variability of el nino strength quantitative estimations of diagenetic photosynthesis pigments derived from absorption band analysis in reflectance spectra are highly correlated to organic carbon content the ratio of pigment fractions is related to chlorine concentration and reflects organic matter preservation and deep water ventilation changes the import of terrigenous mineroclastics tm by local rivers is semi quantitatively documented in the spectrum continuum tm is inversely varying with organic matter preservation and chlorine concentration

source parameters of two ml 5 earthquakes near anza california and a comparison with an imperial valley aftershock strong motion records were used to determine the seismic moments source dimensions and stress drops for two earthquakes near the proposed anza seismic gap thatcher et al 1975 along the san jacinto fault the 25 february 1980 m l 5 5 event and the shock of 15 june 1982 m l 4 8 seismic moments determined for the two events were 2 5 10 23 and 1 1 10 23 dyne cm respectively the source radii were estimated from the displacement pulse widths using the source model of madariaga 1976 static stress drops for the 1980 and 1982 earthquakes were calculated as 110 and 100 bars respectively stress drops determined from the rms accelerations using the method of hanks and mcguire 1981 were 220 bars for the 1980 earthquake and 180 bars for the 1982 event the long period seismic moments for these events derived from regional recordings of 30 to 40 sec love waves were a factor of two to three greater than the moments estimated from the strong motion records as a comparison to the anza events source parameters were also determined from strong motion records for an immediate aftershock m l 5 0 of the 1979 imperial valley earthquake the seismic moment of this aftershock was calculated as 4 2 10 23 dyne cm and its static stress drop was 130 bars static stress drops calculated from the displacement pulse shapes for the three events studied in this paper as well as for an aftershock of the oroville earthquake reported by fletcher et al 1980 exhibit a relatively narrow range between about 100 and 180 bars this result indicates that the stress drops of the two main shocks near anza were not unusually high relative to those of certain aftershocks in other tectonic settings in california