palaeomagnetic and rock magnetic reliability criteria in ophiolitic rocks a case study from the palaeozoic ballantrae ophiolite scotland abstract palaeomagnetic studies of the ballantrae ophiolite southwest scotland are assessed in the light of palaeomagnetic and rock magnetic reliability criteria the remanence directions are palaeomagnetically reliable but have only limited significance for apparent polar wander path construction rock magnetic reliability criteria are found to be ambiguous when treated in isolation original grain size effects are detected in magnetic properties across three sections through pillow lavas we propose that a systematic study of spatial magnetic property variations within pillow lavas can provide an additional field test in the assessment of reliability thermomagnetic analyses and microscopic observations suggest three remanence carrying magnetic phases exist within the extrusive layer of the ophiolite these are almost pure magnetite hematite and titanomaghemite palaeomagnetic rock magnetic and geological observations are best satisfied by a pre obduction magnetisation age this study links the remagnetisation of an ultra oceanic conglomerate to local hydrothermal circulation rather than to a pervasive remagnetisation event as previously suggested

homogeneous moment magnitude calibration in switzerland an earthquake catalog containing a uniform size estimate is important for long term seismic hazard assessment in regions of low to moderate seismicity during the update of the earthquake catalog of switzerland ecos we performed regression analyses to convert all earthquake size information in ecos to physically meaningful moment magnitude m w for 34 events in and near switzerland we determined seismic moment thus m w by regional waveform inversion independent m w estimates for the same events do not exist however m w from european mediterranean events obtained in the same way agree with m w from harvard cmt solutions all other size estimates m l m d m b m s and intensities are calibrated relative to these 34 events teleseismic m s and m b from international data centers are directly regressed against m w most observations in ecos consist of local magnitudes m l m d and intensities for local magnitudes we first calibrated the swiss seismological service s m l then we calibrated magnitudes from observatories in neighboring countries france germany italy using only events in the border region e g france switzerland modern instrumental records exist only since the mid 1970s we calibrated the macroseismic dataset which represents by far the largest period in the catalog by determining surface wave magnitude m s for stronger twentieth century swiss earthquakes from analog seismograms these m s which were converted to m w connect intensities and m w after calibration all 20 300 events in ecos have a unified m w including a class type uncertainty estimate based on the original magnitude scale ecos covers the period 250 2001 from 44 n to 51 n and 4 e to 13 e the largest event in ecos is the 1356 m w 6 9 basle earthquake

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

supercycle at the ecuadorian subduction zone revealed after the 2016 pedernales earthquake large earthquakes are usually assumed to release all of the strain accumulated since the previous event implying a reduced seismic hazard after them however long records of seismic history at several subduction zones suggest supercycle behaviour where centuries long accumulated strain is released through clustered large earthquakes resulting in an extended period of enhanced seismic hazard here we combine historical seismology results present day geodesy data and dense local observations of the recent mw 7 8 2016 pedernales earthquake to reconstruct the strain budget at the ecuador subduction zone since the great 1906 earthquake we show that the pedernales earthquake involved the successive rupture of two patches on the plate interface that were locked prior to the earthquake and most probably overlaps the area already ruptured in 1942 by a similar earthquake however we find that coseismic slip in 2016 exceeds the deficit accumulated since 1942 the seismic moment of every large earthquake during the twentieth century further exceeds the moment deficit accumulated since 1906 these results together with the seismic quiescence before 1906 highlighted by historical records and marine palaeoseismology argue for an earthquake supercycle at the ecuador colombia margin this behaviour which has led to an enhanced seismic hazard for 110 years is possibly still going on and may apply to other subduction zones that recently experienced a great earthquake large earthquakes are often assumed to reset the seismic hazard of a region analysis of recent and historical seismicity in ecuador suggests that this region may experience clusters of large earthquakes and extended periods of high seismic hazard

control of ocean temperature on jakobshavn isbrae s present and future mass loss author s bondzio jh morlighem m seroussi h wood mh mouginot j abstract 2018 american geophysical union all rights reserved large uncertainties in model parameterizations and input data sets make projections of future sea level rise contributions of outlet glaciers challenging here we introduce a novel technique for weighing large ensemble model simulations that uses information of key observables the approach is robust to input errors and yields calibrated means and error estimates of a glacier s mass balance we apply the technique to jakobshavn isbrae using a model that includes a dynamic calving law and closely reproduce the observed behavior from 1985 to 2018 by forcing the model with ocean temperatures only our calibrated projection suggests that the glacier will continue to retreat and contribute about 5 1 mm to eustatic sea level rise by 2100 under present day climatic forcing our analysis shows that the glacier s future evolution will strongly depend on the ambient oceanic setting

foreshock rates from aftershock abundance the question whether foreshocks behave like mainshocks that happen to have larger aftershocks is important for the understanding of earthquake nucleation and the modeling of earthquake clustering many models including the short term earthquake probability step model for forecasting short term earthquake hazard in california and the epidemic type aftershock sequence etas model for the description of earthquake clustering imply that all earthquakes of magnitude m including foreshocks can trigger earthquakes according to a magnitude dependent triggering ability 10 m the magnitudes of the triggered earthquakes are proportional to 10 bm according to the gutenberg richter relation for the magnitude frequency distribution and therefore can be larger than the magnitude of the initiating event however numerous studies observe a lower foreshock occurrence than predicted from aftershock models in this article we show that for homogeneous earthquake catalogs and a consistent definition of foreshocks and aftershocks foreshock rates can be predicted from aftershock characteristics for southern california the probability that the initiating event of an earthquake cluster in the magnitude range 2 0 4 5 is followed by at least one larger event within one day is around 4 this agrees well with corresponding data from the global centroid moment tensor cmt catalog where the probability that the initiating earthquake of a cluster is followed by at least one larger event within 30 days is around 3 these foreshock rates are significantly lower than previously reported and we discuss possible reasons for this

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

locations and magnitudes of historical earthquakes in the sierra of ecuador 1587 1996 summary the whole territory of ecuador is exposed to seismic hazard great earthquakes can occur in the subduction zone e g esmeraldas 1906 mw 8 8 whereas lower magnitude but shallower and potentially more destructive earthquakes can occur in the highlands this study focuses on the historical crustal earthquakes of the andean cordillera several large cities are located in the interandean valley among them quito the capital 2 5 millions inhabitants a total population of 6 millions inhabitants currently live in the highlands raising the seismic risk at present precise instrumental data for the ecuadorian territory is not available for periods earlier than 1990 beginning date of the revised instrumental ecuadorian seismic catalogue therefore historical data are of utmost importance for assessing seismic hazard in this study the bakun wentworth method is applied in order to determine magnitudes locations and associated uncertainties for historical earthquakes of the sierra over the period 1587 1976 an intensity magnitude equation is derived from the four most reliable instrumental earthquakes mw between 5 3 and 7 1 intensity data available per historical earthquake vary between 10 quito 1587 intensity vi and 117 riobamba 1797 intensity iii the bootstrap resampling technique is coupled to the b w method for deriving geographical confidence contours for the intensity centre depending on the data set of each earthquake as well as confidence intervals for the magnitude the extension of the area delineating the intensity centre location at the 67 per cent confidence level 1 depends on the amount of intensity data on their internal coherence on the number of intensity degrees available and on their spatial distribution special attention is dedicated to the few earthquakes described by intensities reaching ix x and xi degrees twenty five events are studied and nineteen new epicentral locations are obtained yielding equivalent moment magnitudes between 5 0 and 7 6 large earthquakes seem to be related to strike slip faults between the north andean block and stable south america to the east while moderate earthquakes mw 6 seem to be associated with to thrust faults located on the western internal slopes of the interandean valley

historical 1942 ecuador and 1942 peru subduction earthquakes and earthquake cycles along colombia ecuador and peru subduction segments two large shallow earthquakes occurred in 1942 along the south american subduction zone inclose proximity to subducting oceanic ridges the 14 may event occurred near the subducting carnegie ridge off the coast of ecuador and the 24 august event occurred off the coast of southwestern peru near the southern flank of the subducting nazca ridge source parameters for these for these two historic events have been determined using long periodp waveforms p wave first motions intensities and local tsunami data we have analyzed thep waves for these two earthquakes to constrain the focal mechanism depth source complexity and seismic moment modeling of thep waveform for both events yields a range of acceptable focal mechanisms and depths all of which are consistent with underthrusting of the nazca plate beneath the south american plate the source time function for the 1942 ecuador event has one simple pulse of moment release with a duration of 22 suconds suggesting that most of the moment release occurred near the epicenter the seismic moment determined from thep waves is 6 8 1020n m corresponding ot a moment magnitude of 7 8 7 9 the reported location of the maximum intensities ix for this event is south of the main shock epicenter the relocated aftershcks are in an area that is approximately 200 km by 90 km elongated parallel to the trench with the majority of aftershocks north of the epicenter in contrast the 1942 peru event has a much longer duration and higher degree of complexity than the ecuador earthquake suggesting a heterogeneous rupture seismic moment is released in three distinct pulses over approximately 74 seconds the largest moment release occurs 32 seconds after rupture initiation the seismic moment as determined from thep waves for the 1942 peru event is 10 25 1020n m corresponding to a moment magnitude of 7 9 8 2 aftershock locations reported by the iss occur over a broad area surrounding the main shock the reported locations of the maximum intensities ix are concentrated south of the epicenter suggesting that at least part of the rupture was to the south we have also examined great historic earthquakes along the colombia ecuador and peru segments of the south american subduction zone we find that the size and rupture length of the underthrusting earthquakes vary between successive earthquake cycles this suggests that the segmentation of the plate boundary as defined by earthquakes this century is not constant

a new 1649 1884 catalog of destructive earthquakes near tokyo and implications for the long term seismic process 1 in order to assess the long term character of seismicity near tokyo we construct an intensity based catalog of damaging earthquakes that struck the greater tokyo area between 1649 and 1884 models for 15 historical earthquakes are developed using calibrated intensity attenuation relations that quantitatively convey uncertainties in event location and magnitude as well as their covariance the historical catalog is most likely complete for earthquakes m 6 7 the largest earthquake in the catalog is the 1703 m 8 2 genroku event seismicity rates from 80 years of instrumental records which include the 1923 m 7 9 kanto shock as well as interevent times estimated from the past 7000 years of paleoseismic data are combined with the historical catalog to define a frequency magnitude distribution for 4 5 m 8 2 which is well described by a truncated gutenberg richter relation with a b value of 0 96 and a maximum magnitude of 8 4 large uncertainties associated with the intensity based catalog are propagated by a monte carlo simulation to estimations of the scalar moment rate the resulting best estimate of moment rate during 1649 2003 is 1 35 1026 dyn cm yr 1 with considerable uncertainty at the 1 level 0 11 0 20 1026 dyn cm yr 1 comparison with geodetic models of the interseismic deformation indicates that the geodetic moment accumulation and likely moment release rate are roughly balanced over the catalog period this balance suggests that the extended catalog is representative of long term seismic processes near tokyo and so can be used to assess earthquake probabilities the resulting poisson or time averaged 30 year probability for m 7 9 earthquakes is 7 11

seismicity associated with the great colombia ecuador earthquakes of 1942 1958 and 1979 implications for barrier models of earthquake rupture abstract we have relocated earthquakes along the colombia ecuador coast with the method of joint hypocenter determination in order to examine the nature of fault heterogeneities that controlled northward propagation of plate boundary rupture from the source region of the earthquake of 14 may 1942 to the source region of the 19 january 1958 earthquake and eventually to the source region of the earthquake of 12 december 1979 the entire region of the 1942 1958 and 1979 shocks had previously ruptured in the single great earthquake of 31 january 1906 the relocated hypocenters lie on the same plane to within the approximately 20 km uncertainty of the focal depths also the main shocks nucleated at nearly the same distance from the colombia trench these observations suggest that the heterogeneities between the 1942 and 1958 ruptures and between the 1958 and 1979 ruptures do not correspond to a major distortion of the downgoing slab but rather to either minor distortions of the slab or to regions of high friction or low available strain energy on a continuous fault surface in particular the heterogeneity between the 1958 and 1979 rupture zones seems to have been a high strength barrier with dimensions much smaller than the dimensions of either of the rupture zones the 1942 and 1958 earthquakes had source dimensions no larger than the 1979 main shock but they had stronger aftershock sequences than the 1979 earthquake this observation suggests that the arrest of earthquake rupture in 1979 left the plate boundary segment that had ruptured in 1906 in a state of lower stress than it had been following the 1942 and 1958 earthquakes long term seismicity in the decades preceding the 1979 earthquake occurred mostly outside or on the boundaries of the rupture area defined by the distribution of 1979 aftershocks the intense aftershock activity that followed the 1958 main shock within tens of kilometers of the eventual 1979 hypocenter may correspond to a long term precursory seismic swarm for the 1979 earthquake

mapping b values in france using two different magnitude ranges possible non power law behavior 1 the first step in probabilistic seismic hazard assessment is the characterization of seismic sources the fundamental assumption is that the gutenberg richter power law can be applied and is valid at all scales in this study we found that the power law model may not be verified in the southeastern regions of france frequency magnitude distributions are mapped using 2 different magnitude ranges 1 3 0 4 4 using only homogeneous instrumental data 2 3 5 m max observed using instrumental and historical data b values estimated on these two magnitude ranges are similar in the pyrenees and the rhine basin however they differ significantly in the southern alps the slopes estimated on magnitude range 3 0 4 4 are much steeper b 1 4 than the slopes estimated on magnitudes above 3 5 0 9 b 1 1 until a clear identification of the underlying processes is made a conservative option i e lowest b values should be considered for probabilistic estimation of hazard in the eastern part of france

earthquake ground effects and intensity of the 16 april 2016 mw 7 8 pedernales ecuador earthquake implications for the source characterization of large subduction earthquakes

seismicity patterns along the ecuadorian subduction zone new constraints from earthquake location in a 3 d a priori velocity model to improve earthquake location we create a 3 d a priori p wave velocity model 3 dvm that approximates the large velocity variations of the ecuadorian subduction system the 3 dvm is constructed from the integration of geophysical and geological data that depend on the structural geometry and velocity properties of the crust and the upper mantle in addition specific station selection is carried out to compensate for the high station density on the andean chain 3 d synthetic experiments are then designed to evaluate the network capacity to recover the event position using only p arrivals and the maxi technique three synthetic earthquake location experiments are proposed 1 noise free and 2 noisy arrivals used in the 3 dvm and 3 noise free arrivals used in a 1 dvm synthetic results indicate that under the best conditions exact arrival data set and 3 dvm the spatiotemporal configuration of the ecuadorian network can accurately locate 70 per cent of events in the frontal part of the subduction zone average azimuthal gap is 289 44 noisy p arrivals up to 0 3 s can accurately located 50 per cent of earthquakes processing earthquake location within a 1 dvm almost never allows accurate hypocentre position for offshore earthquakes 15 per cent which highlights the role of using a 3 dvm in subduction zone for the application to real data the seismicity distribution from the 3 d maxi catalogue is also compared to the determinations obtained in a 1 d layered vm in addition to good quality location uncertainties the clustering and the depth distribution confirm the 3 d maxi catalogue reliability the pattern of the seismicity distribution a 13 yr record during the inter seismic period of the seismic cycle is compared to the pattern of rupture zone and asperity of the mw 7 9 1942 and the mw 7 7 1958 events the mw 8 8 1906 asperity patch is not defined we observe that the nucleation of 1942 1958 and 1906 events coincides with areas of positive simple bouguer anomalies and areas where marine terraces are still preserved on the coastal morphology from north to south 1 the 1958 rupture zone is almost aseismic and is attributed to a zone of high coupling 2 south of the galera alignment perpendicular to the trench the 1942 rupture zone presents moderate seismicity deeper on the seismogenic interplate zone and abutting on the jama cluster to the south this cluster is facing the cabo pasado cap and positive bouguer anomalies on the overriding margin we suspect that this cluster reflects a zone of local asperity partial coupling south of the jama cluster the spherical aseismic zone in the bahia area is interpreted as having a low seismic coupling steady creep motion or slow slip events we suspect that the site that generated the three m 7 events 1896 1956 and 1998 correspond to a small patch of strong coupling to the south in the manta puerto lopez zone the seismicity is mainly organized in earthquake swarms 1998 2002 2005 although slow slip events have been observed in the area vallee et al submitted we infer from the coastline shape the marine terraces and the high positive bouguer anomalies that the seismicity here might reveal a significant amount of seismic coupling

can strong motion observations be used to constrain probabilistic seismic hazard estimates abstract because of the new regulatory requirements that hazards have to be estimated in probabilistic terms the number of probabilistic hazard studies conducted has recently been increasing the present study aims at defining the possibilities and limits for comparing predictions from these studies and observations comparison tests based directly on the rate of ground motion occurrences are favored over the rate of earthquake occurrences based on the properties of poisson processes the minimum time window ensuring reliable occurrence rate estimates at a site is computed and evaluated for example for ground motions with a 475 yr return period at a site a minimal 12 000 yr observation time window is required for estimating the rate with a 20 uncertainty coefficient of variation standard deviation divided by the mean these values are not dependent on the seismicity level of the regions under study an analysis of recorded ground motions at the stations of the permanent french accelerometer network shows that at best the occurrence rates can be estimated with an accuracy of 30 for very low acceleration levels 0 0001 0 001 g for the station stet the same analysis carried out at two stations with longer recording histories and located in higher seismicity regions greece and california provides ground motion levels up to 0 1 g therefore the question posed is can the results of a comparison test at low acceleration levels be generalized to higher acceleration levels even if using a ground motion prediction equation uniformly valid for a wide range of accelerations

distribution of discrete seismic asperities and aseismic slip along the ecuadorian megathrust abstract a dense gps network deployed in ecuador reveals a highly heterogeneous pattern of interseismic coupling confined in the first 35 km depth of the contact between the subducting oceanic nazca plate and the north andean sliver interseismic models indicate that the coupling is weak and very shallow 0 15 km in south ecuador and increases northward with maximum found in the rupture areas of large mw 7 0 megathrust earthquakes that occurred during the 20th century since the great 1906 mw 8 8 colombia ecuador earthquake may have involved the simultaneous rupture of three to six asperities only one or two asperities were reactivated during the large seismic sequence of 1942 mw 7 8 1958 mw 7 7 1979 mw 8 2 and 1998 mw 7 1 the axis of the carnegie ridge which is entering the subduction zone south of the equator coincides well with the location of a 50 km wide creeping corridor that may have acted as persistent barrier to large seismic ruptures south of this creeping region a highly locked asperity is found right below la plata island while this asperity may have the potential to generate an mw 7 0 7 5 earthquake and a local tsunami until now it is unknown to have produced any similar events that region is characterized by the presence of slow slip events that may contribute significantly to reduce the long term moment deficit accumulated there and postpone the failure of that asperity at the actual accumulation rate a characteristic recurrence time for events such as those in 1942 1958 and 1979 is 140 30 yr 90 20 yr 153 80 yr respectively for the great 1906 event we find a recurrence time of at least 575 100 yr making the great 1906 earthquake a rare super cycle event

an earthquake catalog for seismic hazard assessment in ecuador building a unified and homogeneous earthquake catalog is a preliminary step for estimating probabilistic seismic hazard in a country ecuador a territory of 600 km 500 km is characterized by an active seismicity both in the shallow crust and in the subduction zone several international and local earthquake catalogs are available covering different time and spatial windows characterized by different magnitude types and uncertainties after a careful analysis of each catalog in particular for completeness and uncertainty levels we propose a priority scheme for merging the instrumental catalogs moreover several historical earthquakes are analyzed to estimate epicentral location and magnitude completing the solutions obtained in a previous publication once the historical earthquakes are appended to the instrumental catalog the resulting catalog covers five centuries in the cordillera region next homogenization of magnitudes and removal of aftershocks is performed different options are studied and the impact on the recurrence curve is evaluated for the cordillera region within 2 5 and 1 latitude the average occurrence of an earthquake with m w 6 0 is 10 20 years based on the historical catalog

complements to magnitudes of large shallow earthquakes from 1904 to 1980 abstract in the previous paper magnitudes of large earthquakes of the world were determined on a very uniform basis and catalogued in order to arrive at a more homogeneous catalogue for a study of global seismicity some complements are presented the major complements are as follows 1 the m s values for the period 1904 1909 in the previous paper were overestimated in the extreme case by 0 5 magnitude units 2 the m b values for the period 1904 1908 in the previous paper were also overestimated 3 the magnitudes of deep and intermediate shocks which are listed in seismicity of the earth by gutenberg and richter are found to be approximated by m b m b 7 4 4 the catalogues of m b for shallow intermediate and deep shocks are continued for the period up to 1980

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

estimating earthquake location and magnitude from seismic intensity data analysis of modified mercalli intensity mmi observations for a training set of 22 california earthquakes suggests a strategy for bounding the epicentral region and moment magnitude m from mmi observations only we define an intensity magnitude m i that is calibrated to be equal in the mean to m m i mean m i where m i mmi i 3 29 0 0206 i 1 68 and i is the epicentral distance km of observation mmi i the epicentral region is bounded by contours of rms m i rms m i m i rms m i m i where rms is the root mean square rms m i m i is the minimum rms over a grid of assumed epicenters and empirical site corrections and a distance weighting function are used empirical contour values for bounding the epicenter location and empirical bounds for m estimated from m i appropriate for different levels of confidence and different quantities of intensity observations are tabulated the epicentral region bounds and m i obtained for an independent test set of western california earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes the analysis strategy is particularly appropriate for the evaluation of pre 1900 earthquakes for which the only available data are a sparse set of intensity observations

partitioning of oblique convergence in the northern andes subduction zone migration history and the present day boundary of the north andean sliver in ecuador along the ecuadorian margin oblique subduction induces deformation of the overriding continental plate for the last 15 ma both exhumation and tectonic history of ecuador suggest that the northeastward motion of the north andean sliver nas was accompanied by an eastward migration of its eastern boundary and successive progressively narrowing restraining bends here we present geologic data earthquake epicenters focal mechanisms gps results and a revised active fault map consistent with this new kinematic model all data sets concur to demonstrate that active continental deformation is presently localized along a single major fault system connecting fault segments from the gulf of guayaquil to the eastern andean cordillera although secondary faults are recognized within the cordillera they accommodate a negligible fraction of relative motion compared to the main fault system the eastern limit is then concentrated rather than distributed as first proposed marking a sharp boundary between the nas the inca sliver and the subandean domain overthrusting the south american craton the nas limit follows a northeast striking right lateral transpressional strike slip system from the gulf of guayaquil isla puna to the andean cordillera and with the north south striking transpressive faults along the eastern andes eastward migration of the restraining belt since the pliocene abandonment of the sutures and reactivation of north south striking ancient fault zones lead to the final development of a major tectonic boundary south and east of the nas favoring its extrusion as a continental sliver accommodating the oblique convergence of the nazca oceanic plate toward south america

seamount subduction at the north ecuadorian convergent margin effects on structures inter seismic coupling and seismogenesis at the north ecuadorian convergent margin 1 s 1 5 n the subduction of the rough nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust we used three selected pre stack depth migrated multi channel seismic reflection lines collected during the sisteur cruise to investigate the margin structure and decipher the impact of the subducted atacames seamounts on tectonic erosion interseismic coupling and seismogenesis in the region of the 1942 mw7 8 earthquake this dataset highlights a subducted 30 40 km 30 40 km double peak seamount that belongs to the atacames seamount chain and that is associated with a deep morphologic re entrant containing mass transport deposits the seamount subduction uplifted the margin basement by 1 6 km and pervasively broke the margin by deep and intense reverse faulting ahead of the seamount a process that is likely to weaken considerably the margin in the seamount wake the basement reverse fault system rotated counter clockwise this faulted basement is overlain with slope sediment sliding along listric normal faults that sole out onto the bsr this superposition of deep tectonic contraction within the basement and shallow gravitational extension deformation within the sediment highlights the key role of gas hydrate on outer slope erosion in addition to long term regional basal erosion the margin basement has thinned locally by an extra 0 8 1 km in response to the subduction of the atacames seamount chain and hydrofracturing by overpressured fluids at the margin toe this pervasively and deeply fractured margin segment is associated with a seismically quiet and gps modeled low interseismic coupling corridor that terminates downdip near the 1942 epicenter and locked zone we suggest that the deeply buried double peak atacames seamount triggered the 1942 earthquake ahead of its leading flank this result supports previous studies proposing that subducted seamounts provide unfavorable conditions for locking the updip segment of the plate boundary limiting the updip extent of seismogenic zones but may favor large subduction earthquakes at greater depths