magnitude scaling of early warning parameters for the mw 7 8 tocopilla chile earthquake and its aftershocks we studied the correlation between the final event magnitude and four parameters obtained from the early portion of p and s phases for a set of high quality subduction events these relationships are used in the framework of earthquake early warning systems for real time magnitude estimation the investigated parameters are thelow pass filteredpeakdisplacement pd theintegralofthevelocitysquared iv2 and the predominant and characteristic periods p and c we created a dataset from the continuous records of the first twoweeks following the 14 november 2007 mw 7 8 tocopilla chile earthquake the dataset includes 69 events with magnitudes greater than 4 among them the main event mw 7 8 the main aftershocks of mw 6 7 occurred on november 15 and 4 events with magnitudegreater than 6 the low pass filtered pd readonshortp phaseands phasewindowsiswellcorrelated withthefinalmagnitude confirming previous results indeed when examining 2 s timewindows of pwaves we didnotobserveanysaturationeffectformagnitudesgreaterthan6 5 however thereisa slope change in the regression curve a similar result is obtained from the integral of squared velocity computed over short windows around p and s waves the character istic and predominant periods are correlated with magnitudes up to mw 6 but they clearly do not scale with the magnitude for the stronger events our observations offer insight into the feasibility of an early warning system in chile

a deep seismic sounding investigation of lithospheric heterogeneity and anisotropy beneath the iberian peninsula abstract the dimensions of the iberian peninsula the facility of firing large charges in the surrounding waters the well known and relatively uniform geology and prior knowledge of the crustal structure resulted in it being chosen as a study area for the investigation of the seismic structure of the lower lithosphere via refraction wide angle reflection seismic profiling the iberian lithosphere heterogeneity and anisotropy experiment iliha with a star shaped arrangement of six long range dss profiles was carried out in october 1989 the models derived from a first interpretation of the recorded data are presented three crustal profiles cover the same western and central part of the hercynian massif as the mantle profiles the resulting interpretations all include a middle as well as a lower crustal layer above the mantle the velocities of the layers in all three models are similar however the layer depths vary beneath the profiles interpretation of the mantle derived data suggests a layered lower lithosphere one reversed line and an intersecting unreversed line indicate the layering penetrates to at least 90 km depth the homogeneity of these layers contrasts strongly with the heterogeneous hercynian surface geology velocities derived from reflected data from the deep layers suggest the constituent materials are either anisotropic or that the layers suffer a slight regional dip

reply to comment by p rydelek et al on earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records 1 based on the analysis of mediterranean near source strong motion records zollo et al 2006 hereinafter referred to as zln showed that peak displacement amplitudes of initial pand s wave seismic signals scales with the earthquake size in the moment magnitude range 4 6 1 9 in figure 1 we report data distribution vs magnitude and hypocentral distance note that the distance distribution of analyzed events for japan figure 1 is clearly different from that for the mediterranean med earthquakes given by zln whereas most of med records occur at an hd 40 km 10 at odds with rwh we did not apply any cut off at m 5 5 on hypocentral distance for small and moderate events indeed this may introduce a bias on the estimation of attenuation law parameters retrieved from both small and large earthquakes records we follow the zln procedure involving among others sensitivity correction p and s phase identification double integration filtering in a frequency band 0 075 3 hz peaks are read on the modulus of displacement expressed in meters starting from the pwave and s wave picked arrivals we measure peaks within a 2 second window for the p arrival we also test the method with 4 second windows 11 the distance attenuation effect is corrected for by assuming a simple log linear model wu and zhao 2006 zln the amplitudes are normalized to a reference distance of 10 km i e the same as for zln in the mediterranean study to facilitate comparison though rwh show data normalized at a distance of 20 km zln figures 2a and 2b the use of a different normalization distance does not change the slope of the log peak vs magnitude relationships and thus does not alter the graphical interpretation 12 in figure 2 we show the relation between the logarithm of distance normalized peak displacement for p and s waves in different time windows vs final magnitude of the events following zln statistical significance was geophysical research letters vol 34 l20303 doi 10 1029 2007gl030560 2007 click here for full article

identification of high frequency pulses from earthquake asperities along chilean subduction zone using strong motion the chilean subduction zone is one of the most active of the world with m 8 or larger interplate thrust earthquakes occurring every 10 years or so on the average the identification and characterization of pulses propagated from dominant asperities that control the rupture of these earthquakes is an important problem for seismology and especially for seismic hazard assessment since it can reduce the earthquake destructiveness potential a number of studies of large chilean earthquakes have revealed that the source time functions of these events are composed of a number of distinct energy arrivals in this paper we identify and characterize the high frequency pulses of dominant asperities using near source strong motion records two very well recorded interplate earthquakes the 1985 central chile ms 7 8 and the 2007 tocopilla mw 7 7 are considered in particular the 2007 tocopilla earthquake was recorded by a network with absolute time and continuos recording from the study of these strong motion data it is possible to identify the arrival of large pulses coming from different dominant asperities the recognition of the key role of dominant asperities in seismic hazard assessment can reduce overestimations due to scattering of attenuation formulas that consider epicentral distance or shortest distance to the fault rather than the asperity distance the location and number of dominant asperities their shape the amplitude and arrival time of pulses can be one of the principal factors influencing chilean seismic hazard assessment and seismic design the high frequency pulses identified in this paper have permitted us to extend the range of frequency in which the 1985 central chile and 2007 tocopilla earthquakes were studied this should allow in the future the introduction of this seismological result in the seismic design of earthquake engineering

new geochemical and palaeontological data from the permian triassic boundary in the south african karoo basin test the synchronicity of terrestrial and marine extinctions abstract the end permian mass extinction epme is widely recognised as the largest mass extinction in phanerozoic history in marine strata the main extinction event is well constrained and has been radiometrically dated to an interval of some 60 kyr approximately 251 9 million years ago however the age and duration of the epme in the terrestrial realm as well as its possible synchronicity with that of the marine realm is debated here we shed light on issues pertaining to the identification and position of the terrestrial epme in southern africa using recently collected sedimentological facies sequences palaeontological biostratigraphic ranges geochemical stable isotope analyses and detrital zircon id tims data from a new site in the xhariep district of the south african karoo basin we demonstrate that the permian triassic boundary sequence containing evidence for phased tetrapod extinctions is time equivalent with the marine extinction we conclude that the terrestrial epme recorded in the karoo may be regarded as essentially synchronous with the epme currently defined in the marine realm and was likely the result of the same volcanically induced atmospheric disturbances this study describes the first single vertical succession of vertebrate and plant fossils that span the terrestrial permian triassic boundary that are also well constrained both by relative stable isotopes and absolute detrital zircon geochronology dating methods

earthquake early warning system in southern italy methodologies and performance evaluation we investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity pgv from moderate to large earthquakes occurring in the southern apennines italy simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the pgv following an evolutionary probabilistic approach the system performance is measured through the effective lead time elt i e the time interval between the arrival of the first s wave and the time at which the probability to observe the true pgv value within one standard deviation becomes stationary and the probability of prediction error ppe which provides a measure of pgv prediction error the regional maps of elt and ppe show a significant variability around the fault up to large distances thus indicating that the system s capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault

the mw 7 7 tocopilla earthquake of 14 november 2007 at the southern edge of the northern chile seismic gap rupture in the deep part of the coupled plate interface the slip distribution of the mw 7 7 tocopilla earthquake was obtained from the joint inversion of teleseismic and strong motion data rupture occurred as underthrusting at the base of the seismically coupled plate interface mainly between 35 and 50 km depth from the hypocenter located below the coast 25 km south of the town of tocopilla the rupture propagated 50 km northward and 100 km southward overall the slip distribution was dominated by two slip patches one near the hypo center and the other 70 km to the south where slip reached its maximum value 3 m an additional branch of moderate slip propagated at shallower depth toward the west near the northern tip of the mejillones peninsula rupture velocity remained close to 2 8 km sec with a total rupture duration of 45 sec the first 2 weeks of aftershocks located with a local seismic network display a strong correlation with the slip distri bution the 2007 rupture ended below the mejillones peninsula where the 1995 an tofagasta rupture also ended ruegg et al 1996 delouis et al 1997 pritchard et al 2006 this corroborates the role of barrier played by this structure the downdip end of the seismically coupled zone at 50 km depth evidenced by previous studies for the 1995 event is also confirmed the 2007 tocopilla earthquake contributed only mod erately to the rupturing of the great northern chile seismic gap which still has the capacity for generating a much larger underthrusting event

intraplate and interplate earthquakes in chilean subduction zone a theoretical and observational comparison abstract during the last decade efforts to improve our knowledge of great chilean earthquakes have shown that not all of the major destructive events have occurred in the contact between the nazca and south american plates interplate earthquakes waveform analysis of records from the ms 8 0 1950 antofagasta and the ms 7 8 1939 chillan earthquakes have shown that these large events are tensional rupturing along nearly vertical intermediate depth fault planes within the subducting slab intraplate events previous studies found that other earthquakes in chile like santiago 1945 ms 7 1 la ligua 1965 ms 7 1 tal tal 1965 ms 6 9 tocopilla 1970 ms 6 5 and tarapaca 2005 mw 7 8 were also of tensional type in the present work we analyze theoretical and observational evidence comparing interplate and intraplate earthquakes we found clear differences in the source characteristics between these two kinds of events with intermediate depth intraplate earthquakes presenting larger corner frequencies and greater seismic energy release than interplate events for a given seismic moment this is also reflected in the higher averaged apparent stress drop for intraplate earthquakes a 90 bar compared to interplate events a 30 bar from theoretical computations we found that the rupture velocity has a minor effect on the resulting displacements while directivity and changes in the static stress drop produced notable and similar results we believe that the differences found in the data might be due to changes in the static stress drop the effect of directivity or both regardless of the cause of the observed differences in the apparent stress drop these results should be taken into consideration into the assessment of the seismic hazard in chile

high resolution relocation and mechanism of aftershocks of the 2007 tocopilla chile earthquake summary we study the distribution of the aftershocks of tocopillamw 7 7 earthquake of 2007 november 14 in northern chile in detail this earthquake broke the lower part of the seismogenic zone at the southern end of the northern chile gap a region that had its last megathrust earthquake in 1877 the aftershocks of tocopilla occurred in several steps the first day they were located along the coast inside the co seismic rupture zone after the second day they extended ocean wards near the mejillones peninsula finally in december they concentrated in the south near the future rupture zone of the michilla intermediate depth earthquake of 2007 december 16 the aftershock sequence was recorded by the permanent ipoc integrated plate boundary observatory in chile network and the temporary task force network installed 2 weeks after the main event a total of 1238 events were identified and the seismic arrival times were directly read from seismograms initially we located these events using a single event procedure and then we relocated them using the double difference method and a crosscorrelation technique to measure time differences for clusters of aftershocks we tested a 1 d velocity model and a 2 d one that takes into account the presence of the subducted nazca plate relocation significantly reduced the width of the aftershock distribution in the inland area the plate interface imaged by the aftershocks is thinner than 2km the two velocity models give similar results for earthquakes under the coast and a larger difference for events closer to the trench the surface imaged by the aftershocks had a length of 160km it extends from 30 to 50km depth in the northern part of the rupture zone and between 5 and 55km depth near the mejillones peninsula we observed a change in the dip angle of the subduction interface from 18 to 24 at a depth of 30km we propose that this change in dip is closely associated with the upper limit of the rupture zone of the main event we also studied the focal mechanisms of the aftershocks most of them were thrust events like the mainshock as the aftershock activity was significantly reduced on 2007 december 13 an ml 6 1 event occurred offshore of the mejillones peninsula reactivating the seismicity three days later the michilla intraslab earthquake of mw 6 8 ruptured an almost vertical fault with slab push mechanism the aftershocks locations of this event define a planar zone about 11km in depth situated right bellow the subduction interface

an automatic phase picker for local and teleseismic events an automatic detection algorithm has been developed which is capable of time p phase arrivals of both local and teleseismic earthquakes but rejects noise bursts and transient events for each signal trace the envelope function is calculated and passed through a nonlinear amplifier the resulting signal is then subjected to a statistical analysis to yield arrival time first motion and a measure of reliability to be placed on the p arrival pick an incorporated dynamic threshold lets the algorithm become very sensitive thus even weak signals are timed precisely during an extended performance evaluation on a data set comprising 789 p phases of local events and 1857 p phases of teleseismic events picked by an analyst the automatic picker selected 66 per cent of the local phases and 90 per cent of the teleseismic phases the accuracy of the automatic picks was ideal i e could not be improved by the analyst for 60 per cent of the local events and 63 per cent of the teleseismic events

new frequency based real time magnitude proxy for earthquake early warning the two frequency based magnitude proxies currently employed by earthquake early warning systems in california are the predominant and the characteristic periods these proxies obtained using simple expressions that are valid for noise free monochromatic signals yield erroneous result the log average period log introduced in this study is calculated directly from the actual velocity spectrum of the first few seconds of the seismic record using data from south california and japan consisting of 440 earthquakes whose magnitudes range between 3 and 7 3 it is demonstrated that log is better correlated with the catalog magnitude than the predominant period and provides better magnitude assessment than the characteristic period for small magnitudes m 4 the average prediction error is reduced with increasing the input interval up to 6 s it appears that a single linear scaling describes the relation between log log and the catalog magnitude for the entire magnitude range studied here

a regional approach for earthquake early warning in south west iberia a feasibility study abstract a spanish alert es project was set up to study the feasibility of setting up an earthquake early warning system to warn of potentially damaging earthquakes that can occur in the cape of san vicente sv gulf of cadiz gc area located in the south west of the iberian peninsula such as the 1755 lisbon earthquake four events located close to the epicenters of the largest earthquakes in the area were simulated using different seismic software packages earthworm seiscomp3 and probabilistic and evolutionary early warning system presto and the errors were analyzed in addition a study about the blind zone and the lead time at six selected targets was carried out the results show a blind zone in the southwest corner of portugal for sv earthquakes and also a blind zone in the coastal area from portimao to cadiz for the gc earthquakes

estimating earthquake magnitude with early arrivals a test using dynamic and kinematic models recent studies on seismological data indicate that earthquake magnitude scales with either the dominant period or the peak amplitude in the seismogram s first few seconds at first sight this may indicate that the earthquake s final size is some how related to the way rupture starts one working hypothesis is that strong radiation from the initial phase of rupture is indicative of a triggering asperity releasing a con sistent amount of elastic energy with the potential to drive the fracture to large extents we tested this concept with a number of numerical simulations but within the models investigated scaling was found only for ruptures extending up to about four times the size of the initial asperity at larger distances the correlation was lost alternatively a careful kinematic analysis of the earthquake source radiation shows that the initial signal recorded at any station does not necessarily correspond to the rupture initiation but may represent an extended portion of the radiating source using the concept of isochrones we show that the apparent scaling may be explained by a simple kinematic model respecting causality up to a given magnitude threshold where the scaling re lation saturates the saturation level is in agreement with that observed in some but not all of the real seismicity catalogs online material additional synthetic kinematic catalogs

spectral scaling of the aftershocks of the tocopilla 2007 earthquake in northern chile summary we study the scaling of spectral properties of a set of 68 aftershocks of the 2007 november 14 tocopilla m 7 8 earthquake in northern chile these are all subduction events with similar reverse faulting focal mechanism that were recorded by a homogenous network of continuously recording strong motion instruments the seismic moment and the corner frequency are obtained assuming that the aftershocks satisfy an inverse omega square spectral decay radiated energy is computed integrating the square velocity spectrum corrected for attenuation at high frequencies and for the finite bandwidth effect using a graphical approach we test the scaling of seismic spectrum and the scale invariance of the apparent stress drop with the earthquake size to test whether the tocopilla aftershocks scale with a single parameter we introduce a non dimensional number that should be constant if earthquakes are self similar for the tocopilla aftershocks cr varies by a factor of 2 more interestingly cr for the aftershocks is close to 2 the value that is expected for events that are approximately modelled by a circular crack thus in spite of obvious differences in waveforms the aftershocks of the tocopilla earthquake are self similar the main shock is different because its records contain large near field waves finally we investigate the scaling of energy release rate gc with the slip we estimated gc from our previous estimates of the source parameters assuming a simple circular crack model we find that gc values scale with the slip and are in good agreement with those found by abercrombie and rice for the northridge aftershocks

p wave attenuation with implications for earthquake early warning several widely implemented and tested earthquake early warning algorithms employ empirical equations that relate earthquake magnitudes with ground motion peak amplitudes and hypocentral distances this approach is effective to the extent that the offline dataset available for setting the fitting coefficients in those equations is of sufficient quality and quantity however to address the problem of having a limited dataset it is instructive to gain physical understanding of the main factors controlling the p wave attenuation in this study theoretical expressions are derived that relate the root mean square rms of the p wave displacement d rms and velocity v rms to the seismic moment stress drop and hypocentral distance the theoretical attenuation laws are then validated against observed attenuation using earthquake data from southern california and japan good agreement is found between observed and predicted ground motions the similar ground motion attenuation in california and japan suggests that the attenuation laws are similarly applicable for the two regions and implies that they may also be implemented in other regions without having to go through a lengthy calibration phase because d rms is more strongly dependent on the seismic moment than v rms use of the attenuation law for d rms yields better magnitude prediction than that of v rms it is shown that the d rms to v rms ratio is proportional to the characteristic length of the rupture and that the stress drop is a function of the seismic moment and the cube of d rms v rms this result paves the way for a new stress drop determination scheme that is totally independent of previously used approaches finally it is shown that the rms of the ground motions are proportional to their peak values

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

accurate hypocentre determination in the seismogenic zone of the subducting nazca plate in northern chile using a combined on offshore network the coupled plate interface of subduction zones commonly called the seismogenic zone has been recognized as the origin of fatal earthquakes a subset of the after shock series of the great antofagasta thrust type event 1995 july 30 mw 8 0 has been used to study the extent of the seismogenic zone in northern chile to achieve reliable and precise hypocentre locations we applied the concept of the minimum 1 d model which incorporates iterative simultaneous inversion of velocity and hypocentre parameters the minimum 1 d model is complemented by station corrections which are influenced by near surface velocity heterogeneity and by the individual station elevations by relocating mine blasts which were not included in the inversion we obtain absolute location errors of 1 km in epicentre and 2 km in focal depth a study of the resolution parameters ale and dspr documents the importance of offshore stations on location accuracy for offshore events based on precisely determined hypo centres we calculate a depth of 46 km for the lower limit of the seismogenic zone which is in good agreement with previous studies for this area for the upper limit we found a depth of 20 km our results of an aseismic zone between the upper limit of the seismogenic zone and the surface correlates with a detachment zone proposed by other studies the results are also in agreement with thermal studies for the antofagasta forearc region

limitation of the predominant period estimator for earthquake early warning and the initial rupture of earthquakes abstract we investigate the characteristics and limitations of the parameter p t which represents the predominant period of the p wave we analyze the effects of the length of the time window tw low pass filter and anelastic attenuation as well as the complexity of the source process to elucidate whether values of or the time dependent maximum value of p t have direct relationships to the physical quantities of earthquakes we find that values of have upper and lower limits for larger earthquakes with source durations longer than the tw the values of have an upper limit that depends on the tw on the other hand the values for smaller earthquakes have a lower limit that is proportional to the sampling interval for intermediate earthquakes the values of are close to their typical source durations and can have a large variety due to the complexity of the source process these two limits and the slope for intermediate earthquakes yield an apparent final size dependence of in a wide magnitude range as a result the dependence of on the final size of earthquakes does not suggest that the final size of an earthquake is controlled by processes in the initial part of rupture it is impossible to conclude whether the earthquake is deterministic or not from the dependence of on the final size of earthquakes this is because does not always have a direct relation to the physical quantities of earthquakes

magnitude estimation using the first three seconds p wave amplitude in earthquake early warning 1 pd is the peak amplitude of displacement in the first three seconds after the arrival of the p wave we investigated the attenuation of pd with the hypocentral distance r in southern california as a function of magnitude m and obtained the following relationship log pd 3 463 0 729 m 1 374 log r 0 305 given an earthquake location determined by the p wave arrival times at stations close to the epicenter this relationship can be used to define a so called pd magnitude of earthquakes our result shows that for earthquakes in southern california the pd magnitudes agree with the catalog magnitudes with a standard deviation of 0 18 for events less than magnitude 6 5 therefore pd is a robust measurement for estimating the magnitudes of earthquakes and has practical application in earthquake early warning systems citation wu y m and l zhao 2006 magnitude estimation using the first three seconds p wave amplitude in earthquake early warning geophys res lett 33 l16312 doi 10 1029 2006gl026871

crustal deformation and fault slip during the seismic cycle in the north chile subduction zone from gps and insar observations summary the different phases of the earthquake cycle can produce measurable deformation of the earth s surface this work is aimed at describing the evolution of that deformation in space and time as well as the distribution of causal slip on the fault at depth we have applied gps and synthetic aperture radar sar interferometry insar techniques to northern chile where fast plate convergence rates are associated with large subduction earthquakes and extensive crustal deformation the region of northern chile between 18 s and 23 s is one of the most important seismic gaps in the world with no rupture having occurred since 1877 in 1995 the mw 8 1 antofagasta earthquake ruptured the subduction interface over a length of 180 km in the region immediately to the south of this 450 km long gap the coseismic deformation associated with this event has been documented previously here we use gps position time series for 40 benchmarks measured between 1996 and 2000 and ers sar interferograms for the interval between 1995 and 1999 to map both the post seismic deformation following the 1995 event and the ongoing interseismic deformation in the adjacent gap region in the seismic gap the interseismic velocities of 20 30 mm yr 1 to the east with respect to south america are mapped both the gps and the insar measurements can be modelled with 100 per cent coupling of the thrust interface of the subduction to a depth of 35 km with a transition zone extending down to 55 km depth the slip rate in that zone increases linearly from zero to the plate convergence rate south of the gap the interferometric map shows interseismic deformation superimposed with deformation following the 1995 earthquake and covering the same area as the coseismic deformation some 40 per cent of this deformation is related to seismic activity in the 3 3 yr following the 1995 event in particular slip during a mw 7 1 earthquake in 1998 however most of the signal 60 per cent corresponds to post seismic deformation resulting from widespread aseismic slip in the subduction interface the afterslip appears to have occurred down dip in the transition zone at 35 55 km depth and to have propagated laterally northwards at 25 45 km depth under the mejillones peninsula which is a prominent geomorphological feature at the boundary between the 1877 and 1995 rupture zones we propose a simple slip model for the seismic cycle associated with the antofagasta earthquake where the transition zone alternates between aseismic shear and seismic slip

the magnesium isotope budget of the modern ocean constraints from riverine magnesium isotope ratios we have measured the magnesium mg isotope ratios in 45 rivers including 16 of the largest rivers in the world covering a range of geologic tectonic and climatic drainage basin environments the range in riverine 26mg is 2 5 half the variation in terrestrial rock although the mg isotopic composition of the source rock is important for small rivers at a global scale lithology is of limited significance for mg isotope ratios in rivers part of the variability at a global scale may be attributed to fractionation in the weathering environment the rivers analysed constitute 30 of the global mg riverine flux to the oceans and a flux weighted mg isotope composition of global runoff has been estimated at 1 09 even taking into account uncertainty this is distinct from seawater at 0 82 this difference arises either from the fractionation of mg isotope ratios in the ocean and or a mg budget which is not at steady state the difference is consistent with fractionation by carbonate precipitation in the simplest steady state scenario where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output mg isotope ratios imply a minimum dolomite mg flux of 9 of the total output mg flux the implications of the distinct isotopic composition of the riverine flux from modern seawater is that the mg isotope ratio of seawater has probably varied outside of current analytical uncertainty mg isotope ratios may therefore provide a valuable new tracer in palaeo oceanography

the mw 8 1 antofagasta north chile earthquake of july 30 1995 first results from teleseismic and geodetic data a strong mw 8 1 subduction earthquake occurred on july 30 1995 in antofagasta northern chile this is one of the largest events during this century in the region it ruptured the southernmost portion of a seismic gap between 18 s and 25 s in 1992 we had used gps to survey a network with about 50 benchmarks covering a region nearly 500 km long n s and 200 km wide e w part of these marks were re surveyed with gps after the 1995 earthquake comparison with 1992 positions indicate relative horizontal displacement towards the trench reaching 0 7 m the inland subsided several decimeters the mejillones peninsula was uplifted by more than 15 cm teleseismic body wave modelling of vbb records gives a subduction focal mechanism and source time function with three distinct episodes of moment release and southward directivity modelling the displacement field using a dislocation with uniform slip in elastic half space suggests a rupture zone with 19 24 eastward dip extending to a depth no greater than 50 km with n s length of 180 km and an average slip of about 5 m the component of right lateral slip inferred both from the teleseismic and geodetic data does not require slip partitioning at the plate boundary that the well constrained northern end of the 1995 rupture zone lies under the southern part of the mejillones peninsula increases the probability for a next rupture in the gap north of it

automatic detection and rapid determination of earthquake magnitude by wavelet multiscale analysis of the primary arrival earthquake early warning systems must save lives it is of great importance that networked systems of seismometers be equipped with reliable tools to make rapid determinations of earthquake magnitude in the few to tens of seconds before the damaging ground motion occurs a new fully automated algorithm based on the discrete wavelet transform detects as well as analyzes the incoming first arrival with great accuracy and precision estimating the final magnitude to within a single unit from the first few seconds of the p wave

predicting the macroseismic intensity from early radiated p wave energy for on site earthquake early warning in italy earthquake early warning systems eews are potentially effective tools for risk mitigation in active seismic regions the present study explores the possibility of predicting the macroseismic intensity within eew timeframes using the squared velocity integral iv2 measured on the early p wave signals a proxy for the p wave radiated energy of earthquakes this study shows that iv2 correlates better than the peak displacement measured on p waves with both the peak ground velocity and the housner intensity with the latter being recognized by engineers as a reliable proxy for damage assessment therefore using the strong motion recordings of the italian accelerometric archive a novel relationship between the parameter iv2 and the macroseismic intensity im has been derived the validity of this relationship has been assessed using the strong motion recordings of the istituto nazionale di geofisica e vulcanologia strong motion data and osservatorio sismico delle strutture databases as well as in the case of the mw 6 29 may 2012 emilia earthquake italy comparing the predicted intensities with the ones observed after a macroseismic survey our results indicate that p wave iv2 can become a key parameter for the design of on site eews capable of proving real time predictions of the im at target sites

seismic potential for large and great interplate earthquakes along the chilean and southern peruvian margins of south america a quantitative reappraisal the seismic potential of the chilean and southern peruvian margins of south america is reevaluated to delineate those areas or segments of the margin that may be expected to experience large or great interplate earthquakes within the next 20 years 1984 2004 long term estimates of seismic potential or the conditional probability of recurrence within a specified period of time are based on 1 statistical analysis of historic repeat time data using weibull distributions and 2 deterministic estimates of recurrence times based on the time predictable model of earthquake recurrence both methods emphasize the periodic nature of large and great earthquake recurrence and are compared with estimates of probability based on the assumption of poisson type behavior the estimates of seismic potential presented in this study are long term forecasts only as the temporal resolution or standard deviation of both methods is taken to range from 15 to 25 of the average or estimated repeat time at present the valparaiso region of central chile 32 35 s has a high potential or probability of recurrence in the next 20 years coseismic uplift data associated with previous shocks in 1822 and 1906 suggest that this area may have already started to rerupture in 1971 1973 average repeat times also suggest this area is due for a great shock within the next 20 years flanking segments of the chilean margin coquimbo illapel 30 32 s and talca concepcion 35 38 s presently have poorly constrained but possibly quite high potentials for a series of large or great shocks within the next 20 years in contrast the rupture zone of the great 1960 earthquake 37 46 s has the lowest potential along the margin and is not expected to rerupture in a great earthquake within the next 100 years in the north the seismic potentials of the mollendo arica 17 18 s and arica antofagasta 18 24 s segments which last ruptured during great earthquakes in 1868 and 1877 are also high but poorly constrained

earthquake magnitude estimation from early radiated energy 1 from inspection of a large set of japanese events we investigate the scaling of the early radiated energy inferred from the squared velocity integral iv2 with the final magnitude of the event we found that the energy can only discriminate whether the event has a magnitude larger or smaller than 5 8 and in the latter case it can allow for real time magnitude estimation however by normalizing iv2 for the rupture area the initial slip scales with the magnitude between 4 m 7 following the expected scaling laws we show that the ratio between the squared peak displacement and iv2 is a proxy for the slip following the same scaling but it can be directly derived from the data without any assumption on the rupture area the scaling relationship between initial slip and magnitude can be used for early warning applications when integrated in a probabilistic evolutionary approach

earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records 1 we show that the low pass filtered peak amplitudes of initial p and s wave seismic signals recorded in the vicinity of an occurring earthquake source correlates with the earthquake magnitude and may be used for real time estimation of the event size in seismic early warning applications the earthquake size can be therefore estimated using only a couple of seconds of signal from the p or s wave onsets i e while the rupture itself is still propagating and rupture dimension is far from complete we argue that dynamic stress release and or slip duration on the fault in the very early stage of seismic fracture scales both with the observed peak amplitude and with the elastic energy available for fracture propagation the probability that a fracture grows to a larger size should scale with the energy initially available citation zollo a m lancieri and s nielsen 2006 earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records geophys res lett 33 l23312 doi 10 1029 2006gl027795

kinematic rupture process of the 2007 tocopilla earthquake and its main aftershocks from teleseismic and strong motion data summary we study a large m w 7 6 earthquake that occurred on 2007 november 14 in the northern chile seismic gap near the city of tocopilla using a variety of seismic data we show that this earthquake ruptured only the lower part of the interplate seismic zone and generated a series of plate interface aftershocks two large aftershocks on 2007 november 15 ruptured the interplate zone oceanwards of the mejillones peninsula a major geographical feature in the antofagasta region on 2007 december 16 a large m w 6 8 aftershock that occurred near the southern bottom of the fault plane of the main event is shown to be a slab push earthquake located inside the subducted nazca plate and triggered by along slab compression aftershocks of this event demonstrate that it occurred on an almost vertical fault the tocopilla earthquake took place just after the installation of a new seismological network by chilean german and french researchers the accelerometric data combined with far field seismic data provide a quite complete and consistent view of the rupture process the earthquake broke a long 130 km and narrow about 30 50 km zone of the plate interface just above the transition zone using a non linear kinematic inversion method we determined that rupture occurred on two well defined patches of roughly elliptical shape we discuss the consequences of this event for models of gap filling earthquakes in chile proposed in the 1970s