evidence of large scale deformation patterns from gps data in the italian subduction boundary abstract we present the velocity field in italy derived from over 300 continuous gps stations operated in the 1998 2009 time span the gps network maps the whole country with a mean inter site distance of about 50 km and provides a valuable source of data to study the ongoing deformation processes in the central mediterranean the estimated horizontal and vertical velocity fields show major significant features and also less known second order kinematic features a general uplift characterizes the whole apennines and alpine belts that follow the topographic ridge whereas the po plain shows a gradually increasing subsidence from west to east the apennines belt displays a distinctive extension 50 80 10 9 yr 1 while compressive tectonic regimes characterize northern sicily eastern alps and the northeast front of the northern apennines 25 50 10 9 yr 1 second order deformation patterns on large scale wavelength 100 km have been detected on the accretionary prism of central and southern apennines that are highly correlated with other geophysical data vp anomalies seismic anisotropy etc and related to deep rooted sections 70 100 km marked by different subduction regimes apparently at this scale length the observed deformations are governed by the lithosphere as a whole we interpret these deformations as a result of different subduction mechanisms such as variations of the subduction rollback velocity affecting different segments of the subduction zone and or to mantle flows in proximity of the slab edges further south in central southern sicily we detect a contraction of 1 1 0 2 mm yr that probably accommodates part of the africa eurasia convergence on the outer thrust front of the apennines maghrebides belt this hypothesis agrees with an independent analysis of the seismicity associated to the sicilian basal thrust thought to be still active the itrf2005 estimates of the new gps velocity field are available also in sinex format as supplementary file s1

space time evolution of crustal deformation related to the mw 6 3 2009 l aquila earthquake central italy from principal component analysis inversion of gps position time series

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

unravelling the complexity of apenninic extensional fault systems a review of the 2009 l aquila earthquake central apennines italy the 2009 l aquila sequence activated a normal fault system 50 km long in the central apennines composed of two main nw trending faults 12 16 km long the main high angle l aquila segment and the campotosto listric fault the mw 6 1 l aquila mainshock nucleated on the paganica fault at a depth of 8 6 km and cut through the upper crust producing coseismic surface slip of up to 10 cm observed along a strike length of 13 km analysis of historical seismicity and data collected in paleo seismological trenches suggest that this event filled a 500 year gap in contrast the blind campotosto listric fault is composed of different fault segments displaying abrupt changes in dip at a depth where major events nucleate suggesting a rheological and geometrical control on stress concentration a foreshock sequence that started around 4 months before the l aquila mainshock activated the deepest portion of the paganica fault and marked the onset of large variations in elastic properties of the crustal volume the variations have been modelled in terms of dilatancy and diffusion processes corroborating the hypothesis that fluids play a key role in the nucleation process of extensional faults in the crust

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

coseismic deformation of the destructive april 6 2009 l aquila earthquake central italy from gps data 1 on april 6 2009 01 32 39 gmt the city of l aquila was struck by a mw 6 3 earthquake that killed 307 people causing severe destruction and ground cracks in a wide area around the epicenter four days before the main shock we augmented the existing permanent gps network with five gps stations of the central apennine geodetic network cageonet bordering the l aquila basin the maximum horizontal and vertical coseismic surface displacements detected at these stations was 10 39 0 45 cm and 15 64 1 55 cm respectively fixing the strike direction according to focal mechanism estimates we estimated the source geometry with a non linear inversion of the geodetic data our best fitting fault model is a 13 15 7 km2 rectangular fault sw dipping at 55 3 1 8 consistent with the position of observed surface ruptures the estimated slip 495 29 mm corresponds to a 6 3 moment magnitude in excellent agreement with seismological data

evidence for localized active extension in the central apennines italy from global positioning system observations to assess how contemporary crustal extension is accommodated in the central apennines we use a new continuous and survey style global positioning system velocity solution and model the velocity field using a bicubic spline interpolation method the partitioning of contemporary deformation over the 100 km wide central apennines belt reveals a pattern of strain accumulation that largely reflects the spatial distribution of historic and recent seismicity the highest gradients of horizontal velocities are observed across those faults associated with m 6 historical earthquakes dislocation modeling shows that interseismic elastic loading in which creep occurs below the seismogenic upper crust on the downdip extensions of historically active faults reproduces the observed velocity gradients the current resolution level of quaternary fault slip rates estimates hinders the comparison with past deformation patterns and in particular the discrimination between 1 migrating episodes of short term focused activity 2 a distributed pattern of simultaneous deformation on parallel fault systems or 3 long term localization of active extension taking into account geomorphological evidence we propose that the geodetically observed deformation spatially corresponds with a long term localization of strain along the long wavelength 100 km topographic bulge caused by its highest gravitation potential energy relative to surrounding lowlands

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

the anatomy of the 2009 l aquila normal fault system central italy imaged by high resolution foreshock and aftershock locations 1 on 6 april 01 32 utc 2009 a mw 6 1 normal faulting earthquake struck the axial area of the abruzzo region in central italy we study the geometry of fault segments using high resolution foreshock and aftershock locations two main sw dipping segments the l aquila and campotosto faults forming an en echelon system 40 km long nw trending the 16 km long l aquila fault shows a planar geometry with constant dip 48 through the entire upper crust down to 10 km depth the campotosto fault activated by three events with 5 0 mw 5 2 shows a striking listric geometry composed by planar segments with different dips along depth rather than a smoothly curving single fault surface the investigation of the spatiotemporal evolution of foreshock activity within the crustal volume where the subsequent l aquila main shock nucleated allows us to image the progressive activation of the main fault plane from the beginning of 2009 the foreshocks activated the deepest portion of the fault until a week before the main shock when the largest foreshock mw 4 0 triggered a minor antithetic segment seismicity jumped back to the main plane a few hours before the main shock secondary synthetic and antithetic fault segments are present both on the hanging and footwall of the system the stress tensor obtained by inverting focal mechanisms of the largest events reveals a ne trending extension and the majority of the aftershocks are kinematically consistent deviations from the dominant extensional strain pattern are observed for those earthquakes activating minor structures

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

gps monitoring and earthquake prediction a success story towards a useful integration abstract we describe a success story at the junction between south eastern alps and external dinarides that has led to an early deployment of gps stations prior to the predicted july 12th 2004 moderate size slovenia krn mountain earthquake the success story consisted in a straightforward integration between a long lasting lithosphere scale rock mechanics experiment along with gps monitoring leading to a physical model of stress evolution and tested earthquake prediction experiment using m8s cn and rtp algorithms to point out the area of the impending earthquake within the alarmed area by the prediction algorithms the lithosphere scale rock mechanics experiment revealed that the location of the 2004 event falls within an area of stress shadow due to the recent 1998 bovec earthquake but is also very close to an area of increased stress due to the long lasting effect of the 1511 event the pre and post 2004 earthquake gps data provided the following results 1 the krn mountain earthquake magnitude has to be increased from mw 5 2 to 5 5 therefore doubling the fault slip in order to provide a better fit to the near field displacements accordingly the rtp 2004 alarm in northern dinarides can be considered a successful prediction now that the magnitude is inside the prediction range 2 the existence of an important amount of aseismic deformation related to such a moderate size earthquake and the feasibility of monitoring these transients 3 the evidence of a resolved acceleration of the strain rates one year prior to the earthquake 4 the robustness of the bayesian approach in detecting discontinuities in the times series their magnitude and statistical significance the discontinuities or jumps in the time series can correspond to coseismic deformation or time dependent deformation such as creeping slow motion strain acceleration and transients in general 5 when integrated with tested earthquake prediction algorithms the capability to forecast earthquakes can be extended to the scale of the active fault systems

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

space time distribution of afterslip following the 2009 l aquila earthquake 1 the inversion of multitemporal dinsar and gps measurements unravels the coseismic and postseismic afterslip slip distributions associated with the 2009 mw 6 3 l aquila earthquake and provides insights into the rheological properties and long term behavior of the responsible structure the paganica fault well resolved patches of high postseismic slip 10 20 cm appear to surround the main coseismic patch maximum slip 1 m through the entire seismogenic layer above the hypocenter without any obvious depth dependent control time series of postseismic displacement are well reproduced by an exponential function with best fit decay constants in the range of 20 40 days a sudden discontinuity in the evolution of released postseismic moment at 130 days after the main shock does not correlate with independent seismological and geodetic data and is attributed to residual noise in the insar time series the data are unable to resolve migration of afterslip along the fault probably because of the time interval six days between the main shock and the first radar acquisition surface fractures observed along the paganica fault follow the steepest gradients of postseismic line of sight satellite displacements and are consistent with a sudden and delayed failure of the shallow layer in response to upward tapering of slip the occurrence of afterslip at various levels through the entire seismogenic layer argues against exclusive depth dependent variations of frictional properties on the fault supporting the hypothesis of significant horizontal frictional heterogeneities and or geometrical complexities we support the hypothesis that such heterogeneities and complexities may be at the origin of the long term variable behavior suggested by the paleoseismological studies rupture of fault patches with dimensions similar to that activated in 2009 appears to have a 500 year recurrence time interval documented by paleoseismic and historical studies in addition to that paleoseismological evidence of large 0 5 m coseismic offsets seems to require seismic events recurring every 1000 2000 years characterized by 1 multisegment linkage 2 surface ruptures larger than in 2009 and 3 complete failure of the 2009 coseismic and postseismic patches

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

california foreshock sequences suggest aseismic triggering process 1 foreshocks are one of the few well documented precursors to large earthquakes therefore understanding their nature is very important for earthquake prediction and hazard mitigation however the triggering role of foreshocks is not yet clear it is possible that foreshocks are a self triggering cascade of events that simply happen to trigger an unusually large aftershock alternatively foreshocks might originate from an external aseismic process that ultimately triggers the mainshock in the former case the foreshocks will have limited utility for forecasting the latter case has been observed for several individual large earthquakes however it remains unclear how common it is and how to distinguish foreshock sequences from other seismicity clusters that do not lead to large earthquakes here we analyze foreshocks of three m 7 mainshocks in southern california these foreshock sequences appear similar to earthquake swarms in that they do not start with their largest events and they exhibit spatial migration of seismicity analysis of source spectra shows that all three foreshock sequences feature lower average stress drops and depletion of high frequency energy compared with the aftershocks of their corresponding mainshocks using a longer term stress drop catalog we find that the average stress drop of the landers and hector mine foreshock sequences is comparable to nearby swarms our observations suggest that these foreshock sequences are manifestations of aseismic transients occurring close to the mainshock hypocenters possibly related to localized fault zone complexity which have promoted the occurrence of both the foreshocks and the eventual mainshock

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

on the scalability of hydrogeochemical factors controlling arsenic mobility in three major inland basins of p r china abstract high as groundwater has been widely found in inland basins of p r china which has posed a serious health risk to the local residents although these inland basins experience the same arid to semiarid climate and are filled with quaternary sediments as concentrations show big variations three inlands basins have been investigated to characterize hydraulic conductivities and geochemistry of the groundwater and sediments and evaluate their controls on dissolved as concentrations dissolved as concentrations ranged between

the preparatory phase of the 2009 mw 6 3 l aquila earthquake by improving the detection capability of low magnitude foreshocks we explored the detection capability of low magnitude earthquakes before the 6 april 2009 mw 6 3 l aquila event by using a matched filter technique and 512 foreshocks as templates we analyzed continuous waveforms from 10 broadband seismic stations in a 60 km radius from the epicenter and for 3 months before the main shock more than 3000 new events mostly located on the main shock fault were detected to define the spatial temporal evolution of micro seismicity the foreshock sequence was active northwest of the mw 6 3 hypocenter in january then migrated toward it at a speed of 0 5 km day in middle of february at that time in a 4 km2 patch close to the main shock nucleation point the cumulative number of earthquakes gradually increased until the mw 6 3 event this patch characterized by a low b value played a key role in controlling the preparation stage to the 2009 l aquila main rupture

rupture history of the 2009 l aquila italy earthquake from non linear joint inversion of strong motion and gps data 1 we image the rupture history of the 2009 l aquila central italy earthquake using a nonlinear joint inversion of strong motion and gps data this earthquake ruptured a normal fault striking along the apennines axis and dipping to the sw the inferred slip distribution is heterogeneous and characterized by a small shallow slip patch located up dip from the hypocenter 9 5 km depth and a large deeper patch located southeastward the rupture velocity is larger in the up dip than in the along strike direction this difference can be partially accounted by the crustal structure which is characterized by a high velocity layer above the hypocenter and a lower velocity below the latter velocity seems to have affected the along strike propagation since the largest slip patch is located at depths between 9 and 14 km the imaged slip distribution correlates well with the on fault aftershock pattern as well as with mapped surface breakages

complete seismic release of tectonic strain and earthquake recurrence in the apennines italy here i compare estimates of tectonic strain rates from dense global positioning system measurements with the seismicity released in the last 500 years in the apennines italy the rates of seismic moment accumulation from geodesy and of historical seismic release by earthquakes agree within the uncertainties ruling out significant aseismic deformation within the considered 400 km long section of the apennines this balance yields an average recurrence interval of 30 75 years for mw 6 5 events without requiring a future earthquake larger than those observed historically mw 7 a minimum estimate of unreleased strain allows mw 6 5 and mw 6 9 events to be released in 35 and 10 of the central southern apennines respectively the definition of the seismic potential for smaller events is more uncertain and their occurrence remains a significant threat throughout the apennines

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

evaluation of recurrence intervals characteristic earthquakes and slip rates associated with thrusting along the coast range central valley geomorphic boundary california abstract a seismically active blind fold and thrust belt underlies the coast range central valley geomorphic boundary crcv california earthquakes associated with this fault system include the 1983 m w 6 5 coalinga and 1985 m w 6 1 kettleman hills events published estimates of the crcv slip rate derived from published studies range from 1 to 10 mm yr and estimated recurrence intervals of coalinga type events range from 200 to 2000 yr relative consistency of geomorphic expression and regional geologic relationships suggests that deformation rates are similar along the 500 km length of the crcv we evaluated historical seismicity to further constrain recurrence interval and slip rate estimates based on structural geology geomorphology and historical seismicity the crcv may comprise 18 to 25 segments from 12 to 57 km in length with most segments between 20 and 30 km the characteristic earthquake for the average length segment may be m w 6 3 to 6 4 or slightly smaller than the coalinga earthquake and the longest segments may yield earthquakes as large as m w 6 8 to 7 1 during the approximately 150 yr period of historical record 11 earthquakes of m w 5 8 to 6 8 of which eight may be characteristic events have taken place on the crcv the characteristic earthquakes appear to have ruptured single segments using the estimates of co seismic rupture length for the 1983 coalinga and 1985 kettleman hills earthquakes to calibrate earlier events the historical earthquake record corresponds to rupture of 32 to 39 of the length of the crcv in 142 yr a recurrence interval of 360 to 440 yr for the average segment combining the recurrence estimates with estimates for co seismic displacement yields slip rates of 1 8 to 8 0 mm yr because recent vlbi studies suggest that the total convergence rate normal to the pacific north american plate boundary at the latitude of the crcv is 3 mm yr the lower end of the slip rate range 1 8 to 3 mm yr is favored for the crcv if these estimates are correct the crcv accommodates most of the plate convergence between the north american and pacific plates indicating that the historical earthquakes efficiently released strain accumulated on the crcv and suggesting that aseismic deformation along the crcv is minor

radiography of a normal fault system by 64 000 high precision earthquake locations the 2009 l aquila central italy case study 1 we studied the anatomy of the fault system where the 2009 l aquila earthquake mw 6 1 nucleated by means of 64 k high precision earthquake locations spanning 1 year data were analyzed by combining an automatic picking procedure for p and s waves together with cross correlation and double difference location methods reaching a completeness magnitude for the catalogue equal to 0 7 including 425 clusters of similar earthquakes the fault system is composed by two major faults the high angle l aquila fault and the listric campotosto fault both located in the first 10 km of the upper crust we detect an extraordinary degree of detail in the anatomy of the single fault segments resembling the degree of complexity observed by field geologists on fault outcrops we observe multiple antithetic and synthetic fault segments tens of meters long in both the hanging wall and footwall along with bends and cross fault intersections along the main fault and fault splays the width of the l aquila fault zone varies along strike from 0 3 km where the fault exhibits the simplest geometry and experienced peaks in the slip distribution up to 1 5 km at the fault tips with an increase in the geometrical complexity these characteristics similar to damage zone properties of natural faults underline the key role of aftershocks in fault growth and co seismic rupture propagation processes additionally we interpret the persistent nucleation of similar events at the seismicity cutoff depth as the presence of a rheological i e creeping discontinuity explaining how normal faults detach at depth