paleoseismology along the 1980 surface rupture of the irpinia fault implications for earthquake recurrence in the southern apennines italy the irpinia fault was the source of the ms 6 9 1980 irpinia earthquake and produced the first unequivocal historical surface faulting in italy trenching of the 1980 fault scarp at piano di pecore a flat intermontane basin about 5 km south of the 1980 instrumental epicenter provides the first data on earthquake recurrence intervals slip per event and slip rate on a major normal fault in the southern apennines fault zone the trenches exposed evidence of four pre 1980 paleoearthquakes that occurred during the past 8600 years a best estimate average recurrence interval is 2150 years although the time interval between individual events varies by as much as a factor of 2 each paleo earthquake is similar to the 1980 surface rupture in amount of slip and style of deformation which suggests that the 1980 event is characteristic for the irpinia fault slip per event values average 61 cm the net vertical displacement of 2 12 2 36 m since 8600 cal year b p observed in the trenches gives a vertical slip rate of 0 25 0 35 mm yr a dip slip rate of 0 29 0 40 mm yr and an extension rate of 0 14 0 20 mm yr although fault behavior data are only available for the irpinia fault they provide a starting point for evaluating earthquake recurrence and rates of deformation in southern apennines they suggest that 1 fault specific earthquake recurrence intervals based on the historical seismic record overestimates the occurrence of large magnitude m7 earthquakes and 2 the holocene rate of extension across the apennines is 1 mm yr the 1980 earthquake and the paleoseismologic observations show that repeated and localized surface faulting occurs in southern apennines and leaves subtle but distinct geomorphic evidence that can be detected with detailed and careful investigation

revised hypocentre and fault rupture geometry for the 1980 november 23 campania basilicata earthquake in southern italy summary the fault rupture nucleation point of the 1980 november 23 campania basilicata earthquake is relocated following the recent identification of 20 km of surface faulting the carpineta and picentini fault scarps in addition to the 15 km previously documented on the marzano and san gregorio faults all of which have nw strike and 60 ne dip this relocation indicates a range of revised origin times and nucleation point positions at 10 12 km depth that are 5 9 km se of previously documented coordinates between 18 34 52 0 0 3 s with latitude 40 724 1 4 km and longitude 15 414 1 4 km preferred and 18 34 52 5 0 3 s with latitude 40 742 1 4 km and longitude 15 373 1 4 km my preferred nucleation point coincides with a downdip projection of the se end of the carpineta fault and indicates that this fault ruptured first rather than the marzano fault as was previously thought with the fault rupture nucleation point adjusted to this new preferred position field and seismological estimates of seismic moment match well both overall and for individual fault scarps and suggest the following sequence of fault rupture subevents the initial fault rupture nucleated at or near the se end of the carpineta fault and propagated nw releasing 2 5 1018 n m seismic moment rupture continued apparently without interruption onto the adjoining marzano fault farther nw where 6 5 1018n m of seismic moment was released rupture then paused for 0 5s before continuing nw along the picentini fault where 4 5 1018n m more seismic moment was released probably early in this sequence of nw propagating ruptures a se propagating rupture released 2 1018 n m seismic moment on the san gregorio fault each of these fault scarps and the corresponding rupture subevent was associated with intense aftershock activity the existence of another aftershock cluster nw of the picentini scarp suggests a fifth mainshock rupture subevent at castelfranci which released up to 2 1018 n m more seismic moment rupture at this locality appears necessary to explain the form of ground acceleration recorded nearby also following these ruptures on steep ne dipping normal faults two additional ruptures occurred on faults with different orientations 20 s and 40 s after the initial mainshock rupture the 40 s subevent involved release of 3 1018 n m of seismic moment on a steep normal fault that dips sw at 70 and projects to the earth s surface 11 km ne of the marzano fault the 20 s subevent apparently involved release of 4 1018 n m of seismic moment on a surface dipping ne at 20 at the base of the brittle upper crust beneath this steep antithetic fault points where normal fault ruptures nucleated on the steep ne dipping normal faults coincide with en echelon steps of 1 km and abrupt 15 changes in strike the marzano and carpineta faults which have strike 315 took up a small component of left lateral slip as is revealed by the first motion focal mechanism teleseismic waveform modelling striations measured in the field and consistent rightward stepping their slip vector azimuth is n37 e assuming the same slip vector azimuth a component of right lateral slip is expected on the san gregorio and picentini faults that have strike 300

application of numerical wave propagation techniques to study local soil effects the case of benevento italy many of the numerical techniques used for seismic zonation studies treat one dimensional structural models and or the incidence of plane polarized body waves these techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest in such cases a more rigorous treatment of the combined effects of the source the path and the site response is needed this can be accomplished with a hybrid approach combining modal summation and the finite difference technique to demonstrate the differences between these techniques the ground motion in the city of benevento italy is modelled we first compare the results obtained with one and two dimensional structural models for vertical incidence of plane polarized body waves these results are then compared with those obtained with the hybrid approach for two dimensional structural models

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

reply to p bernard and a zollo s comment on source complexity of the 1980 southern italian earthquake from the analysis of strong motion s wave polarization

a contribution to seismic hazard assessment in croatia from deterministic modeling some of the elements of regional seismic hazard in croatia are assessed by computing synthetic accelerograms at a predetermined set of sites the input dataset consists of structural models parameters of seismic sources and an updated earthquake catalog synthetic strong motion time series for frequencies below 1 hz are computed on a grid of sites using the modal summation technique the long period hazard is described by the distribution of estimated peak values of ground displacement velocity and acceleration while the short period hazard is represented by the map of design ground acceleration values dga the highest values of dga exceeding 0 35 g on the base rock level are found in the southeastern coastal part of the country in the greater dubrovnik area

mid to late holocene coastal environmental changes in southwest florida usa during the holocene florida experienced major changes in precipitation and runoff to better understand these processes shallow marine sediment cores from charlotte harbor southwest florida were studied covering approximately the past 9000 years whole core xrf scanning was applied to correlate different sediment cores on a river to sea transect biomarkers were used to identify periods with increased runoff and primary productivity the mid holocene sediments are characterized by a relatively large input of terrestrially derived organic matter with a maximum in precipitation and runoff around 5 kyr bp this maximum can be linked to large scale changes in the hydrological cycle involving shifts of the itcz bermuda azores high and polar front around 3 5 kyr bp charlotte harbor changed from a runoff dominated environment to a more oligotrophic and marine setting although other studies suggest that around this time precipitation in florida increased this is not reflected by the charlotte harbor

strong motion modeling of the imperial valley earthquake of 1979 twelve three component strong motion displacement records are modeled for the 1979 imperial valley earthquake to recover the distribution of slip on the imperial fault plane the final model for which point source responses are calculated by a discrete wavenumber finite element technique uses a structure with gradients in material properties rather than layers the effects of a velocity gradient are investigated by comparing synthetics with a layer over a half space model using generalized rays it is shown that a uniform fault rupture model on a rectangular fault plane does not explain the data the preferred fault model has slip concentrated below 5 km in the basement material and between the epicenter 5 km south of the international border and highway 80 within this region there appears to be two localized areas of larger dislocations one just north of the border near bonds corner and a second under interstate 8 at meloland overpass a major arrival associated with large amplitude vertical accelerations up to 1 7 g is identified in the el centro array records this arrival has an s p time of approximately 2 3 sec at many of the array stations and is modeled as originating from a localized source 8 km to the south of the array the moment is estimated to be 5 0 10 25 dyne cm from the strong motion records which is consistent with teleseismic body wave estimates the preferred fault model is strike slip with a 90 dip the average strike is 143 however to explain vertical waveforms near the fault trace a corrugated or wiggly fault plane is introduced the average rupture velocity is in the range 2 5 to 2 7 km sec 0 8 to 0 9 times the basement shear wave velocity the preferred model has unilateral rupture propagation to the north although the data would allow a small amount of propagation to the south the estimated stress drop for the entire fault plane is only 5 to 10 bars however the stress drop over the more localized sources is about 200 bars the fault model is consistent with the pattern of seismicity and observations of aseismic creep in the imperial valley and suggests that the southern half of the imperial fault acts as a locked section which breaks periodically

seismic ground motion in napoli for the 1980 irpinia earthquake the seismic ground motion in the urban area of napoli has been computed for the 1980 earthquake m s 6 9 with a hybrid technique based on the mode summation and the finite difference methods the detailed geological setting of each quarter has been reconstructed from several stratigraphies and six geological zones have been recognized shear wave velocity profiles have been assigned based on hole tests and inversion of rayleigh group velocities artificially generated

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

irpinia italy 1980 earthquake waveform modelling of strong motion data summary several strong motion records of the irpinia southern italy 1980 earthquake have been modelled for a total time duration of about 180 s with the use of the rnultimode summation of waves of p sv and sh type if waveform modelling is applied to unfiltered accelerations the best that can be done at present is amplitude envelope matching in time and frequency domain the early phase of the studied event can be synthesized by 12 main episodes of different sizes modelling the rupturing process the space time distribution of such episodes suggests that the rupturing process did propagate in a bilateral fashion this model of the seismic source gives rise to synthetic velocity records which match quite well the experimental ones to avoid the problems connected with the large instability of displacements obtained from direct numerical integration of observed accelerograms the synthetic signals can be first used to perform acceleration or velocity fitting of experimental data an estimate of the ground displacement above 1 hz can then be obtained by analytical integration of the synthetic velocities

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

an inversion method to analyze the rupture processes of earthquakes using near field seismograms a new and very practical nonlinear least square inversion method has been developed to investigate the dislocation distribution and the character of rupture propagation on an earthquake fault plane the problem is parameterized using a model in which the fault is composed of subfaults which start rupturing with arbitrary magnitudes at arbitrary times the performance of the method is examined by numerical simulations and the method proves useful for the analysis of source processes of earthquakes including complicated cases such as multiple events the source process of the naganoken seibu earthquake of 1984 has been analyzed using strong motion seismograms the dislocation distribution and the character of rupture propagation have been successfully obtained

linearized inversion for fault rupture behavior application to the 1984 morgan hill california earthquake we present a technique to infer the rupture history of an earthquake from near source records of ground motion unlike most previous studies each point on the fault is assumed to slip only once when the rupture front passes with a spatially variable slip intensity in this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture time we perform a linearized inversion for slip intensity and rupture time by iteratively perturbing an assumed starting model the inverse problem for the model perturbation is solved using a tomographic back projection technique smoothing and inequality constraints are applied to ensure that the resulting solution is stable and feasible asymptotic ray theory is used to calculate theoretical seismograms and partial derivatives with respect to model parameters in test cases with noisy synthetic data sets we found that it is possible to distinguish between rupture models having variable slip amplitude and models having variable rupture velocity provided the station coverage is adequate we apply the technique to recordings of the april 24 1984 morgan hill earthquake the results indicate that slip amplitude on the fault plane was extremely variable and that the rupture front did not propagate uniformly away from the hypocenter in particular rupture was delayed on a 12 km2 section of the fault approximately 14 km to the southeast of the hypocenter the rupture front surrounded the region which subsequently failed with a component of rupture propagation back toward the hypocenter similar behavior has been observed in dynamic rupture models with stress or strength inhomogeneities this segment of the fault ruptured with a large slip amplitude releasing 12 of the total seismic moment from 4 of the total area of the aftershock zone the surface trace of this section of the fault is characterized by a complex left step that could act to increase the normal stress acting across the fault however the distribution of aftershocks suggests that the fault at depth is simpler and that it may bend to the right in either case our rupture model suggests that this segment of the fault represents an asperity which initially resisted rupture but eventually ruptured massively we estimate the shear fracture energy for this earthquake to be 2 106 j m2

a new asymptotic method for the modeling of near field accelerograms we study high frequency radiation from a dislocation model of rupture propagation at the earthquake source we demonstrate that in this case all the radiation emanates from the rupture front and by a change of variables that at any instant of time the high frequency waves reaching an observer come from a line on the fault plane that we call isochrone an asymptotic approximation to near source velocity and acceleration is obtained that involves a simple integration along the isochrones for every time step it is shown that wave front discontinuities critical or stopping phases are radiated every time an isochrone becomes tangent to a barrier this leads to what we call the critical ray approximation which is given in a closed form the previous results are compared with discrete wavenumber synthetics obtained by bouchon 1982 for the gilroy 6 recording of the coyote lake earthquake of 1980 the fit between the asymptotic and full numerical method is extremely good the critical ray approximation permits the identification of different phases in bouchon s synthetics and the prediction of the behavior of the signal in the vicinity of their arrival time

signal processing and spectral analysis of the aftershocks of the 1980 el asnam algeria earthquake engineering application abstract seismic recording stations were set up in the el asnam region of algeria by the department of nuclear safety of the french atomic energy commission cea ipsn after the severe october 10 1980 earthquake to study the aftershocks of this important event three of these stations equipped with sma 1 instruments were intended to record strong ground motion and were accordingly installed near the trace of the fault responsible for the main shock three other more sensitive stations were placed in such a way as to make up a small network enclosing the central portion of this fault over 400 events were thus recorded during october and november 1980 of which certain events presented accelerations of nearly 0 2g the sma 1 recordings were used as a basis for comparing different methods of correcting time histories demonstrating the influence of the digitization rate especially upon the high frequency elements of the ground acceleration and that of the type of low frequency filtering upon the integrated velocity and displacement time histories the most significant recordings from both types of station were processed and their response spectra computed from recordings of the same earthquake obtained on a massive concrete slab and in the free field a marked filtering effect in the high frequency range is to be observed

the campania lucania southern italy earthquake of 23 november 1980 abstract we present the main seismological results of our study of the campania lucania earthquake of 23 november 1980 a complete set of far field and local data has been analysed from long period body waves data we determine the fault plane solution 1 140 1 60 2 75 2 54 a depth of 15 km and calculate a seismic moment of 6 1025 dyne cm and a source duration of 6 s from data of a local network deployed immediately after the event we determine aftershock locations they are aligned in a direction nw se that fit extremely well with the focal solution determined above we can choose as fault plane the plane striking 140 and dipping at 60 and the event is a normal event with a large component of left lateral strike slip the source area evaluated from this aftershock distribution 14 km 40 km is quite suitable for an earthquake of a seismic moment of 6 1025 dyne cm

update and sensitivity analysis of the neo deterministic seismic hazard assessment for egypt abstract the main goal of this work is to provide an update on the seismic hazard maps available for egypt that incorporates the results of recent studies i e revised historical earthquake catalogs morphostructural zonation data mz revised focal mechanism solutions and mechanical models of the lithospheric structure this is done within the framework of the neo deterministic seismic hazard assessment ndsha procedure that may effectively accommodate any reliable new information to adequately compute the earthquake ground motion maps i e pga pgv and pgd furthermore with the set of relevant scenario earthquakes this work provides a large dataset of synthetic seismograms particularly important for the areas that suffer from the endemic lack of useful strong motion time histories such as egypt setting the base toward detailed and comprehensive seismic microzonation studies ndsha aims to supply an envelope value in other words a value that should not be exceeded therefore it is immediately falsifiable and verifiable a sensitivity analysis based on the different ground motion maps computed adopting different a models for the earthquake source process b mechanical models of the crust and c mapmaker s preconceptions e g different seismotectonic models is provided the maps of difference and ratio between various ground motion maps computed for different variants are shown and discussed in order to explore the influence of using various input models the results provide the potential users with an adequate spectrum of choices and reliably assess and clearly communicate the possible uncertainties the availability of a wide spectrum of hazard maps is a prerequisite to supply valuable information for the significant improvement of a seismic code

aftershocks of the campania lucania italy earthquake of 23 november 1980 abstract the result of a study of 1130 aftershocks of the 1980 campania lucania earthquake are presented the data were collected primarily with a dense array of portable smoked drum seismographs deployed in the epicentral region a few days after the main shock tests performed on subsets of the data to establish the location accuracy are described in detail and epicentral maps and cross sections are presented and discussed one hundred and sixty well constrained fault plane solutions using upward traveling rays are presented the distribution of aftershocks forms an elongate cloud which does not define a plane this is not because the events are poorly located a subset of events located with epicentral errors of less than 1 km and depth errors less than 2 km forms a similar cloud to the complete aftershock set the aftershock mechanisms are very varied some are similar to the main event but many differ profoundly these include events on shallow or vertical planes and thrust events the latter include some events which require contraction in the direction in which the main event indicates extension the aftershocks of all mechanisms are intermixed in space in such a way that no simple system of faults can explain them a model to explain the aftershocks and the lack of surface ruptures in the main event is offered it is proposed that the main shock cuts between two aseismic detachment surfaces and that the aftershocks are a consequence of the complicated deformation that such a geometry demands whatever interpretation is adopted the results are a challenge to the commonly accepted view that aftershocks even approximately define simple fault planes or that aftershock mechanisms replicate the mechanism of the main shock defects in interpretations of the main shock and aftershocks process arise largely from a lack of information about the geometry of structures at depth in the epicentral region suitable deep reflection profiles could help to resolve this problem

bromine counts from xrf scanning as an estimate of the marine organic carbon content of sediment cores 1 xrf sediment core scanning technology is increasingly used to quantify sediment composition the overall good correlation between biophilic halogen bromine br and sedimentary total organic carbon toc potentially allows the fast estimation of down core toc profiles by xrf scanning in order to test this approach we present data from the arabian sea and a mediterranean brine basin comparing xrf core scanning br data with discrete sample toc analyses overall br counts and toc show a clear correlation except when stable carbon isotope and c n data indicate intervals characterized by enhanced input of terrestrial organic matter hence solid phase br is exclusively associated with marine organic matter moc and can be used as a direct estimate of this parameter after a calibration is established high pore water br in the brine core steepens the br toc correlation but after salt correction shows a nearly identical gradient to that of the arabian sea core

detailed study of the potentino seismic zone in the southern apennines italy abstract most relevant macroseismic and instrumental data concerning past and current seismic activity of the potentino southern italy have been collected in order to study the seismic behaviour of this area ten among the most important recent and historical earthquakes occurred in the area from 1826 to 1990 have been studied by means of macroseismic methodologies macroseismic fields for all the events indicate a general isoseismal lengthening in the direction of the apennines chain northwest southeast a rapid attenuation of intensity westward of the studied area and a strong propagation eastwards this configuration is strongly dependent on the source mechanisms of the seismic events and the geological dishomogeneities of the concerned areas as regards earthquakes which have been instrumentally recorded in the campania basilicata area from 1980 to 1991 more than 1300 accurate hypocentral locations have been computed for events with m d 2 5 using data from osservatorio vesuviano o v and istituto nazionale di geofisica i n g seismic networks special emphasis is put on the potenza may 5 1990 earthquake m s 5 4 neic national earthquake information center i vii msk which was the strongest recent event in the area and was felt in a large sector of southern italy as regards the seismic sequence following this event about 110 aftershocks with m d 1 9 have been located very close to the town of potenza northeast of it with a clustering type space distribution the occurrence of the events is strongly time concentrated in so defining a main shock aftershocks typical sequence moreover the macroseismic investigation of the main event has allowed to map out isoseismal lines bounding vii vi v and iv msk areas the isoseismals pattern shows that attenuation and amplification of intensity are observed in the same areas as for the previous events beginning from may 26 1991 an increase of seismicity initiated by an earthquake of m l 4 7 neic and i vi vii msk was observed nearly in the same area as the 1990 sequence accurate locations of 84 events with m d 1 9 have been computed however this sequence seems to have a slightly different character from the 1990 one in that events are scattered in time and seismic energy release is comparable to a swarm type seismic sequence as regards the previous sequences fault plane solutions for the highest magnitude events and for appropriate groups of events have been worked out the mechanisms indicate normal faulting motion with t axes oriented orthogonal to the apenninic chain in conclusion detailed analyses on the historical and recent seismicity of the potentino area and adjacent ones have allowed to identify at least four seismogenic zones which show activity with different features such zoning represents a contribution to the seismic hazard assessment in the southern apennines on a regional scale

mechanisms of enso forcing of hemispherically symmetric precipitation variability summary the patterns of precipitation anomalies forced by the el nino southern oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and in the mid latitudes have a prominent zonally symmetric component observations of global precipitation variability and the moisture budget within atmospheric reanalyses are examined to argue that the zonally symmetric component is caused by interactions between transient eddies and tropically forced changes in the subtropical jets during el nino events the jets strengthen in each hemisphere and shift equatorward changes in the subtropical jet influence the transient eddy momentum fluxes and the eddy driven mean meridional circulation during el nino events eddy driven ascent in the mid latitudes of each hemisphere is accompanied by low level convergence and brings increased precipitation this changes in the transient eddy and stationary eddy moisture fluxes almost exactly cancel each other and in sum do not contribute to the zonal mean precipitation anomalies propagation of anomalous stationary waves disrupts the zonal symmetry flow around the deeper aleutian low and the eastward extension of the pacific jet stream supply the moisture for increased precipitation over the eastern north pacific and the western seaboard of the united states while transient eddy moisture convergence supplies the moisture for increased precipitation over the southern united states in each case increased precipitation is fundamentally caused by anomalous ascent forced by anomalous heat and vorticity fluxes

new paleoseismic data from the irpinia fault a different seismogenic perspective for southern apennines italy abstract the irpinia fault i e mount marzano fault system mmfs was responsible for the devastating 1980 earthquake mw 6 9 that caused the longest surface faulting ever observed in italy 30 km early paleoseismological studies have revealed a 2 kyr recurrence time for 1980 like characteristic earthquakes on this fault system during the holocene however this appears to clash with both the catastrophic historical seismicity and high gps derived strain rate of the area to explain this apparent discrepancy we investigated the mmfs through a multidisciplinary approach first on the basis of recent archives and archaeological research we reassessed the historical seismicity of the area analysing the highest intensity distribution of the major earthquakes of the upper ofanto valley with respect to the mmfs hanging wall then we carried out a step by step survey along the entire 43 km long fault system through both high precision topographic levelling along the compound fault scarp and geostructural analyses finally we excavated trenches and pits across different fault segments to explore the recent paleoseismological history of the structure based on the combined results that we have obtained we propose a different point of view concerning the seismogenic behaviour of the mmfs from the holocene to the present at the end fault parameters have been compared with those of all the apennines active faults and cross checked with the newest gps results in peninsular italy providing some relevant observation of the relationships between seismogenesis and geodetic deformation

source mechanisms of twenty six large shallow earthquake ms 6 5 during 1980 from p wave first motion and long period rayleigh wave data source mechanisms of 26 large shallow earthquakes are determined in terms of a double couple point source with a correction for the nondirectional part of source finiteness by using p wave first motions and long period rayleigh wave spectra recorded on wwssn ida and gdsn networks the combined use of both data sets allows us to determine the double couple mechanism uniquely in most cases constrained linear moment tensor inversion m xz m yz 0 correctly determines the strike of the fault but fails to estimate the dip and underestimates the scalar moment all thrust events along the deep sea trenches analyzed in this study show nodal planes which dip perpendicular to the trench axis at an angle shallower than 45 the fit to data of the double couple inversion is comparable to that of the constrained moment tensor inversion using the phase spectra of surface waves we can detect a slow source process with an accuracy of about 10 to 20 sec

use of long period surface waves for rapid determination of earthquake source parameters 2 preliminary determination of source mechanisms of large earthquakes ms 6 5 in 1980 an inversion method for fast retrieval of earthquake source parameters developed earlier has been applied to 28 large m s 6 5 shallow earthquakes which occurred in 1980 rayleigh waves recorded by the ida international deployment of accelerographs network were used for the analysis for very shallow events the inversion is ill conditioned and two of the moment tensor elements m zx and m zy are unresolvable of the 28 events a solution is obtained for 25 with the constraints m zx m zy 0 although these constraints limit the solution to be either vertical strike slip or 45 dip slip the method provides a useful first approximation to the mechanism solution for deeper events all of the elements of the moment tensor can be determined after the seismograms have been retrieved the solution can be obtained in 10 min for most events the method would be adequate for preliminary cataloging purposes

the southern italy earthquake of 23 november 1980 an unusual pattern of faulting abstract a complex rupture history for the 23 november 1980 magnitude 6 9 italian earthquake resulted in an unusual pattern of two high angle subperpendicular normal faults forming the corner of a down dropped crustal block evidence for this interpretation is from aftershocks the pattern of strong ground motion focal mechanism of the mainshock and two critically placed leveling profiles quantitative modeling of leveling profiles using smoothly varying dislocation segments provides confirmation of the fault pattern and specific verification of the existence of a secondary fault which is suborthogonal to the primary fault rupture began on the nw trending main fault with downward motion of the northeast block about 40 sec after initial motion began rupture initiated on an orthogonal ne trending subsidiary fault propagating away from the main fault this fault pattern is consistent with tectonic extension in a northeasterly direction

spatial and temporal variability of holocene temperature in the north atlantic region the early holocene climate of the north atlantic region was influenced by two boundary conditions that were fundamentally different from the present the presence of the decaying laurentide ice sheet lis and higher than present summer solar insolation in order to assess spatial and temporal patterns of holocene climate evolution across this region we collated quantitative paleotemperature records at sub millennial resolution and synthesized their temporal variability using principal components analysis pca the analysis reveals considerable spatial variability most notably in the time transgressive expression of the holocene thermal maximum htm most of the region but especially areas peripheral to the labrador sea and hence closest to the locus of lis disintegration experienced maximum holocene temperatures that lagged peak summer insolation by 1000 3000 years many sites from the northeastern north atlantic sector including the nordic seas and scandinavia either warmed in phase with maximum summer insolation 11 000 9000 years ago or were less strongly lagged than the baffin bay labrador sea region these spatially complex patterns of holocene climate development which are defined by the pca resulted from the interplay between final decay of the lis and solar insolation forcing

interacting loop current variability and mississippi river discharge over the past 400 kyr the loop current mediating the oceanic heat and salt flux from the caribbean sea into the atlantic ocean and its interference with the mississippi river discharge are critical for both the regional climate in the gulf of mexico area and the water vapor transport towards high northern latitudes we present a 400 kyr record of sea surface temperature and local surface salinity from the northeastern gulf of mexico images core md02 2575 approximated from combined planktonic foraminiferal 18o and mg ca which reflects the temporal dynamics of the loop current and its relationship to both varying mississippi discharge and evolution of the western hemisphere warm pool the reconstructed sea surface temperature and salinity reveal glacial interglacial amplitudes that are significantly larger than in the western hemisphere warm pool sea surface freshening is observed during the extreme cool periods of marine isotope stages 2 8 and 10 caused by the strengthened mississippi discharge which spread widely across the gulf favored by the less established loop current interglacial and interstadial sea surface conditions instead point to a strengthened northward flowing loop current in line with the northward position of the intertropical convergence zone allowing northeastern gulf of mexico surface hydrographic conditions to approach those of the caribbean at these times the mississippi discharge was low and deflected westward promoted by the extended loop current previously described deglacial megadischarge events further to the west did not affect the northeastern gulf of mexico hydrography implying that meltwater routing from the laurentide ice sheet via the mississippi river is unlikely to have affected atlantic meridional overturning circulation

moment and duration of shallow earthquakes from love wave modelling for regional distances abstract love waves from five earthquakes in southwest germany italy yugoslavia greece and algeria as recorded at the broadband grafenberg array in eastern bavaria are modelled in detail using an extended reflectivity method the focal mechanisms are taken from the literature or determined from long period wwnss data the theoretical double couple moment function used for modelling increases smoothly during the risetime t from zero to the seismic moment m0 t and m0 are determined by matching the observed and theoretical love wave seismograms in the long period wwnss frequency band t is approximately equal to the rupture duration values from 1 4 to 20 s are found seismic moments generally agree within a factor of about two with those found by other authors from larger data sets the earthquakes in southwest germany and greece were simple events and can be modelled very well by one double couple in the case of the other earthquakes the theoretical love wave seismograms are too short for these earthquakes there is some independent evidence for a multiple event nature this evidence is condensed into source models consisting of two or three double couples representing separate and complete sub earthquakes which then explain the observations quite well in the case of the algerian earthquake the long love wave duration may also be due to complications in structure along the wavepath across the mediterranean and the alps the present results show that accurate love wave modelling for a single station at regional distance from an epicentre is a reliable method for estimation of seismic moment and rupture duration use of a digitally recording station with large dynamic range allows events over a large magnitude interval to be studied the grafenberg array is well suited for such an investigation of european and north african earthquakes

the irpinia italy 1980 earthquake detailed analysis of a complex normal faulting a detailed analysis of near source strong motion and leveling data together with the results of teleseismic waveform modeling by westaway and jackson 1987 and aftershock studies by deschamps and king 1984 allows a satisfactory kinematic description of the complex normal faulting associated with the magnitude ms 6 9 november 23 1980 irpinia earthquake southern italy the three main rupture episodes starting at about 0 20 and 40 s are here associated with better constrained source parameters than in previous studies we first evaluated the triggering time for the 11 closest accelerometers by using the well recorded 40 s strong motion phases this gave the absolute time and location of the dominant episodes of faulting the first rupture propagated mainly toward the northwest on a ne dipping normal fault at a mean velocity close to 3 km s for about 20 km and continued 15 km further on smaller subfaults it was associated with surface breakage in the southeastern part the second rupture started from the southeastern end of the first rupture about 18 s after it and propagated about 20 km toward the southeast on a low angle normal fault dipping 20 ne it was associated with secondary faulting on steeper planes reaching the surface the third and last episode at 39 s nucleated near the first hypocenter at shallower depth and the rupture possibly propagated on a 10 to 15 km long normal fault striking se antithetic to the first activated fault a clear correlation appears between the strength of the geological formations and the existence of surface breakage and shallow aftershock activity

millennial to century scale variability in gulf of mexico holocene climate records of the intertropical convergence zone itcz related to orbital forcing the d 18 o of the surface dwelling planktic foraminifer globigerinoides ruber show negative excursions between 14 and 10 2 ka radiocarbon years that reflect influx of meltwater into the western gom during melting of the laurentide ice sheet the relative abundance of the planktic foraminifer globigerinoides sacculifer is related to transport of caribbean water into the gom maximum transport of caribbean surface waters and moisture into the gom associated with a northward migration of the average position of the itcz occurs between about 6 5 and 4 5 ka in addition abundance variations of g sacculifer show century scale variability throughout most of the holocene the gom record is consistent with records from other areas suggesting that century scale variability is a pervasive feature of holocene climate the frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability indicating that at least some of the century scale climate variability during the holocene is due to external solar forcing index terms 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic 3030 marine geology and geophysics micropaleontology

large and rapid climate variability during the messinian salinity crisis evidence from deuterium concentrations of individual biomarkers during the messinian 6 m y ago massive sea level fall and widespread deposition of evaporites occurred in the mediterranean sea when it became isolated from the world oceans here we present the first hydrogen isotope data from individual sedimentary biomarkers n alkanes and isoprenoids that tracked climatically driven hydrographic changes in response to extreme evaporation during the messinian salinity crisis the stable hydrogen and carbon isotope compositions of these biomarkers show a range of 160 in d values and 14 in 13 c values and roughly covary this indicates that the source waters of the biomarkers were therefore in some cases extremely enriched in deuterium having average d as great as 66 vsmow vienna standard mean ocean water such values are only known from desert climates today because the offset between the d values of n alkanes and isoprenoids preserved in the miocene sedimentary rocks is similar to the offset found in modern biological samples we conclude that diagenesis did not significantly affect the primary deuterium concentrations

surface faulting in the southern italian campania basilicata earthquake of 23 november 1980 the campania basilicata earthquake of 23 november 1980 was the largest ms 6 9 and most destructive earthquake that has occurred in this region of southern italy for over 100 years killing more than 3 000 people the consensus among seismologists geologists and earthquake engineers who have studied1 10 this event is in keeping with previous italian earthquakes that it did not produce faulting at the surface this has led to the establishment of a number of models2 3 11 13 requiring an unusual tectonic setting for the southern apennines however on a recent visit to the epicentral region of the earthquake may 1984 we discovered more than 10 km of surface faulting that is consistent with focal mechanisms for this event based on first motion polarities2 4 5 12 and long period waveform studies14 16 which show that it involved normal faulting with one nodal plane dipping at 60 towards the north east our observations of this the first well documented earthquake fault break to be reported in italy suggest that the deformation associated with earthquakes in the southern apennines takes place in the upper 10 15 km of the earth s crust on steep planar normal faults which break the surface as is widely observed in other areas of active extension outside italy

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

on the inverse problem for earthquake rupture the haskell type source model in order to gain insight into how to invert seismograms correctly to estimate the details of the earthquake rupturing process we perform numerical experiments using artificial data generated for an idealized faulting model with a very simple rupture and moment release history and solve the inverse problem using standard widely used inversion methods we construct synthetic accelerograms in the vicinity of an earthquake for a discrete analog of the haskell type rupture model with a prescribed rupture velocity in a layered medium a constant level of moment is released as the rupture front passes by we show that using physically based constraints such as not permitting back slip on the fault allows us to reproduce many aspects of the solution correctly whereas the minimum norm solution or the solution with the smallest first differences of moment rates in space and time do not reproduce many aspects for the cases studied here with the positivity of moment rate constraint as long as the rupturing area is allowed to be larger than that in the forward problem it is correctly found for the simple faulting model considered in this paper provided that the rupture velocity and the earth structure are known if however the rupture front is constrained either to propagate more slowly or the rupturing area is taken smaller than that in the forward problem we find that we are unable even to fit the accelerograms well use of incorrect crustal structure in the source region also leads to poor fitting of the data in this case the proper rupture front is not obtained but instead a ghost front is found behind the correct rupture front and demonstrates how the incorrect crustal structure is transformed into an artifact in the solution the positions of the centroids of the moment release in time and space are generally correctly obtained

rupture history of the 1984 morgan hill california earthquake from the inversion of strong motion records near source strong motion velocity records and teleseismic short period p waveforms are modeled to obtain the spatial and temporal distribution of slip for the 1984 morgan hill earthquake both forward modeling and constrained least squares inversion techniques are used to interpret the strong motion velocity waveforms in the frequency range of approximately 0 2 to 2 0 hz these data support a nearly unilateral rupture to the southeast with a rupture propagation velocity of nine tenths of the local s wave velocity the majority of the slip occurs over a fault length of 25 km and to a first approximation can be interpreted as two main source regions each with an extent of about 5 km with their centers separated by about 12 km however each of the sources has detailed structure of its own and a simple two point source model is not an accurate representation of the morgan hill earthquake the second source occurs about 4 5 sec after the first and is approximately 3 times larger the maximum dislocation on the fault plane is about 1 m the total moment of the earthquake is estimated to be 2 1 10 25 dyne cm the morgan hill earthquake offers convincing evidence for very inhomogeneous slip and stress distributions on shallow strike slip faults

earthquake source time function from coherent and incoherent rupture abstract theoretical study has been made investigating the seismic source spectrum generated from a coherent and incoherent rupture an earthquake is modeled by a finite propagating rupture on a fault plane where fault heterogeneities fault patches are randomly distributed the dislocation velocity of such a fracture is assumed to be approximated by a stochastic process of random impacts of particles obeying brownian motion the parameters of the present stochastic source are seismic moment fault dimension fault patch intensity and patch fracture time the model predicts two corner frequencies one originates from the fault finiteness and the other from the fracturing of fault patches the seismic source spectrum from the model consequently shows distinct frequency dependence of 0 2 2 with increasing angular frequency where is about 1 0 the seismic moment is controlled by an average dislocation on the fault and by the fault dimension the short period spectrum which is much more abundant than that of the ordinary deterministic models is controlled by the product of the fault patch intensity and the square root of their total number the 2 high frequency asymptote of the theoretical spectrum is in conformity with the white acceleration spectrum usually found in the literature and it guarantees the finite total energy of the rupture process