the emplacement of geochemically distinct groups of rhyolites during the evolution of the lower rhyolitic tuff formation caldera ordovician north wales u k rhyolites in the vicinity of snowdon north wales are intimately associated with the evolution of the lower rhyolitic tuff formation lrtf caldera of ordovician caradoc age they occur as deep seated dykes sills and small stocks shallow level intrusive domes and domes extruded within a predominantly shallow marine environment extrusion occurred during three main phases indicating the episodic availability of rhyolite magma the rhyolites can be divided on their trace element ratios e g nb zr into five main groups extrusive representatives indicate that each group correlates strongly with a single phase of rhyolite extrusion within each group the distribution and variation of intrusive form with stratigraphic level suggests that geochemically similar rocks were emplaced at approximately the same time consequently the groups represent discrete magma compositions tapped from the evolving snowdon subvolcanic magma system differences in distribution of the groups reflect changes in structural controls of emplacement before and after development of the lrtf caldera

large pre digital earthquakes of the bonin mariana subduction zone 1930 1974 abstract the bonin mariana subduction zone is the end member example of a decoupled system as described by uyeda and kanamori 1979 with no interplate thrust solutions of moments greater than 8 10 25 dyn cm known in the cmt catalog although a number of earthquakes are reported with assigned magnitudes around or above 7 both during the wwssn period and the historical pre 1962 era we present a systematic study of these events including relocation and inversion of moment tensors we obtain 15 new moment tensor solutions featuring a wide variety of focal mechanisms both in the fore arc and the outer rise and most importantly a shallow dipping interplate thrust mechanism with a moment of 4 10 27 dyn cm for the event of 28 december 1940 at a location 175 km east of pagan our results show that the modern cmt catalog still undersamples the seismicity of the mariana arc which is thus not immune to relatively large albeit rare interplate thrust events with moments 40 times that of the largest global cmt solution frequency magnitude relations would then suggest a return time of 320 years for a magnitude 8 interplate thrust faulting earthquake in the bonin mariana system

seismological analyses of the 2010 march 11 pichilemu chile mw 7 0 and mw 6 9 coastal intraplate earthquakes on 2010 march 11 a sequence of large shallow continental crust earthquakes shook central chile two normal faulting events with magnitudes around m w 7 0 and m w 6 9 occurred just 15 min apart located near the town of pichilemu these kinds of large intraplate inland crustal earthquakes are rare above the chilean subduction zone and it is important to better understand their relationship with the 2010 february 27 m w 8 8 maule earthquake which ruptured the adjacent megathrust plate boundary we present a broad seismological analysis of these earthquakes by using both teleseismic and regional data we compute seismic moment tensors for both events via a w phase inversion and test sensitivities to various inversion parameters in order to assess the stability of the solutions the first event at 14 hr 39 min gmt is well constrained displaying a fault plane with strike of n145 e and a preferred dip angle of 55 sw consistent with the trend of aftershock locations and other published results teleseismic finite fault inversions for this event show a large slip zone along the southern part of the fault correlating well with the reported spatial density of aftershocks the second earthquake 14 hr 55 min gmt appears to have ruptured a fault branching southward from the previous ruptured fault within the hanging wall of the first event modelling seismograms at regional to teleseismic distances 10 is quite challenging because the observed seismic wave fields of both events overlap increasing apparent complexity for the second earthquake we perform both point and extended source inversions at regional and teleseismic distances assessing model sensitivities resulting from variations in fault orientation dimension and hypocentre location results show that the focal mechanism for the second event features a steeper dip angle and a strike rotated slightly clockwise with respect to the previous event this kind of geological fault configuration with secondary rupture in the hanging wall of a large normal fault is commonly observed in extensional geological regimes we propose that both earthquakes form part of a typical normal fault diverging splay where the secondary fault connects to the main fault at depth to ascertain more information on the spatial and temporal details of slip for both events we gathered near fault seismological and geodetic data through forward modelling of near fault synthetic seismograms we build a kinematic k 2 earthquake source model with spatially distributed slip on the fault that to first order explains both coseismic static displacement gps vectors and short period seismometer observations at the closest sites as expected the results for the first event agree with the focal mechanism derived from teleseismic modelling with a magnitude m w 6 97 similarly near fault modelling for the second event suggests rupture along a normal fault m w 6 90 characterized by a steeper dip angle dip 74 and a strike clockwise rotated strike 155 with respect to the previous event

crustal scale structural architecture in central chile based on seismicity and surface geology implications for andean mountain building 1 we document a crustal scale structural model for the central chile andes based on seismicity and surface geology which consists in a major east verging ramp detachment structure connecting the subduction zone with the cordillera the ramp rises from the subducting slab at 60 km depth to 15 20 km below the western edge of the cordillera extending eastward as a 10 km depth flat detachment this structure plays a fundamental role in the andean orogenesis because most of the shortening has been accommodated by structures rooted in it and allows the distribution of crustal thickening in a simple shear deformation mode indeed despite shortening distribution being very asymmetric 16 km versus 70 km in the western and eastern side respectively the western side is higher and thicker than what is expected yield strength envelopes show strong rheological control on this structure vp and vp vs variations in the upper mantle and in the deepest limit of the seismogenic interplate contact mark the intersection of the ramp with the slab which coincides with the blueschist eclogite transition therefore subduction processes would control the depth where the major east verging structure may merge with the slab such a ramp flat structure is observed in other parts of the chilean margin hence it seems to be a first order feature in the andean subduction zone this structure delimitates upward the rocks transmitting part of the plate convergence stress from the plate interface and controls mountain building tectonics thus playing a key role in the andean orogeny

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

a spatial random field model to characterize complexity in earthquake slip 1 finite fault source inversions reveal the spatial complexity of earthquake slip over the fault plane we develop a stochastic characterization of earthquake slip complexity based on published finite source rupture models in which we model the distribution of slip as a spatial random field the model most consistent with the data follows a von karman autocorrelation function acf for which the correlation lengths a increase with source dimension for earthquakes with large fault aspect ratios we observe substantial differences of the correlation length in the along strike a x and downdip a z directions increasing correlation length with increasing magnitude can be understood using concepts of dynamic rupture propagation the power spectrum of the slip distribution can also be well described with a power law decay i e a fractal distribution in which the fractal dimension d remains scale invariant with a median value d 2 29 0 23 while the comer wave number k c which is inversely proportional to source size decreases with earthquake magnitude accounting for larger slip patches for large magnitude events our stochastic slip model can be used to generate realizations of scenario earthquakes for near source ground motion simulations

aftershock seismicity of the 27 february 2010 mw 8 8 maule earthquake rupture zone on 27 february 2010 the mw 8 8 maule earthquake in central chile ruptured a seismic gap where significant strain had accumulated since 1835 shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity here we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines by processing the seismic data between 15 march and 30 september 2010 from stations from iris ipgp gfz and university of liverpool we determined 20 205 hypocentres with magnitudes mw between 1 and 5 5 seismic activity occurs in six groups 1 normal faulting outer rise events 2 a shallow group of plate interface seismicity apparent at 25 35 km depth and 50 120 km distance to the trench with some variations between profiles along strike the aftershocks occur largely within the zone of coseismic slip but extend 50 km further north and with predominantly shallowly dipping thrust mechanisms along dip the events are either within the zone of coseismic slip or downdip from it depending on the coseismic slip model used 3 a third band of seismicity is observed further downdip at 40 50 km depth and further inland at 150 160 km trench perpendicular distance with mostly shallow dipping 28 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture and presumably above the intersection of the continental moho with the plate interface 4 a deep group of intermediate depth events between 80 and 120 km depth is present north of 36 s within the maule segment a large portion of events during the inter seismic phase originated from this depth range 5 the magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mw 8 8 maule 2010 earthquake 6 pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of pichilemu 34 5 s these crustal events occur in a 30 km wide region with sharp inclined boundaries and oriented oblique to the trench the best located events describe a plane dipping to the southwest consistent with one of the focal planes of the large normal faulting aftershock mw 6 9 on 11 march 2010

aftershock seismicity of the 2010 maule mw 8 8 chile earthquake correlation between co seismic slip models and aftershock distribution 1 the 27 february 2010 maule chile mw 8 8 earthquake is one of the best instrumentally observed subduction zone megathrust events here we present locations magnitudes and cumulative equivalent moment of the first 2 months of aftershocks recorded on a temporary network deployed within 2 weeks of the occurrence of the mainshock using automatically determined onset times and a back projection approach for event association we are able to detect over 30 000 events in the time period analyzed to further increase the location accuracy we systematically searched for potential s wave arrivals and events were located in a regional 2d velocity model additionally we calculated regional moment tensors to gain insight into the deformation history of the aftershock sequence we find that the aftershock seismicity is concentrated between 40 and 140 km distance from the trench over a depth range of 10 to 35 km focal mechanisms indicate a predominance of thrust faulting with occasional normal faulting events increased activity is seen in the outer rise region of the nazca plate predominantly in the northern part of the rupture area further down dip a second band of clustered seismicity showing mainly thrust motion is located at depths of 40 45 km by comparing recent published mainshock source inversions with our aftershock distribution we discriminate slip models based on the assumption that aftershocks occur in areas of rapid transition between high and low slip surrounding high slip regions of the mainshock

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

source study and tectonic implications of the historic 1958 las melosas crustal earthquake chile compared to earthquake damage abstract the 4 september 1958 earthquake has been the largest event recorded at shallow depths in the western flank of the andes on chilean territory new estimates of fault orientation depth and size have been carried out using modern techniques of body wave modeling two possible fault planes solutions with right lateral displacement on an east west fault or left lateral displacement on a north south fault nucleated at 5 9 km depth produce the best fit to teleseismic recordings a seismic moment m0 of 0 227 1019 n m associated with a moment magnitude mw of 6 3 has been estimated with these techniques which is a more reliable estimation of earthquake size than the 0 4 0 7 units larger surface wave magnitude ms earlier reported although no surface rupture for the 1958 las melosas crustal earthquake was reported the displacement along east west structures like that one suggested for one of the fault plane in our focal mechanism solution seems to be an efficient mechanism to accommodate differences in shortening from north to south in the high andean cordillera reports on damage landslide effects as well as re analysis of intensities associated with the new seismic source estimations for the 1958 las melosas earthquake are presented to further estimate the hazard to which this zone and others along the western foothills of the andes is exposed

active faulting in northern chile ramp stacking and lateral decoupling along a subduction plate boundary two large features parallel to the coastline of northern chile have long been suspected to be the sites of young or active deformation 1 the 700 km long coastal scarp with average height above sea level of about 1000 m 2 the atacama fault zone that stretches linearly for about 1100 km at an average distance of 30 50 km from the coastline new field observations combined with extensive analysis of aerial photographs demonstrate that both the coastal scarp and the atacama fault are zones of quaternary and current fault activity little degraded surface breaks observed in the field indicate that these fault zones have recently generated large earthquakes m 7 8 normal fault offsets observed in marine terraces in the coastal scarp at mejillones peninsula require tectonic extension roughly orthogonal to the compressional plate boundary strike slip offsets of drainage observed along the salar del carmen and cerro moreno faults atacama fault system imply left lateral displacements nearly parallel to the plate boundary the left lateral movement observed along the atacama fault zone may be a local consequence of e w extension along the coastal scarp but if also found everywhere along strike left lateral decoupling along the atacama fault zone would be in contradiction with the right lateral component of nazca south america motion predicted by models of present plate kinematics clockwise rotation with left lateral slicing of the andean orogen south of the arica bend is one way to resolve this contradiction the coastal scarp and the atacama fault zone are the most prominent features with clear traces of activity within the leading edge of continental south america the great length and parallelism of these features with the subduction zone suggest that they may interact with the subduction interface at depth we interpret the coastal scarp to be a west dipping normal fault or flexure and propose that it is located over an east dipping ramp stack at the subduction interface the similar flexure at the western edge of the altiplano may have the same origin ramp stacking along the subduction zone a mechanism disregarded so far may be an important thickening process in the andes and perhaps the basic cause of the uplift of the altiplano

pervasive cracking of the northern chilean coastal cordillera new evidence for forearc extension despite convergence across the strongly coupled seismogenic interface between the south american and nazca plates the dominant neotectonic signature in the forearc of northern chile is arc normal extension we have used 1 m resolution ikonos satellite imagery to map nearly 37 000 cracks over an area of 500 km2 near the salar grande 21 s these features which are best preserved in a ubiquitous gypcrete surface layer have both nontectonic and tectonic origins however their strong preferred orientation perpendicular to the plate convergence vector suggests that the majority owe their formation to approximate east west extension associated with plate boundary processes such as interseismic loading coseismic and postseismic strain and long term instability resulting from subduction erosion similar structures were formed during or shortly after the 1995 mw 8 0 earthquake near the city of antofagasta south of salar grande and in conjunction with the 2001 mw 8 2 8 4 arequipa peru event cracks such as these may form in other forearcs but remain largely unexposed because of vegetative cover or marked fluvial erosion factors that are absent in northern chile as a result of its hyperarid climate

permanent fore arc extension and seismic segmentation insights from the 2010 maule earthquake chile 1 geologists have long known that young normal faults are an important structural element of the andean coastal cordillera but their relationship to the subduction seismic cycle is still unclear some of the largest aftershocks of the 2010 mw 8 8 maule earthquake in central chile were nucleated on upper plate normal faults including the mw 6 9 and 7 0 events of the pichilemu earthquake sequence we use the available coseismic gps displacements moment tensor sums and slip distribution models for the maule earthquake to compute the static strain and stress fields imposed on the upper plate by slip on the subduction interface the extensional strains calculated from coseismic gps and from a moment tensor sum of the pichilemu events have similar orientations and orders of magnitude the normal coulomb stress increment csi on the pichilemu fault has maximum positive stresses as high as 4 9 mpa regionally the maule event produced a semi elliptical radial pattern of static extension and deviatoric tension csi 1 5 mpa along the coastal cordillera enclosing the rupture area this elliptical pattern mimics the trends of the major upper crustal structures the static deformation field produced by a great subduction earthquake is an effective mechanism for generating permanent extension above the seismogenic zone reactivating suitably oriented long lived normal faults we suggest that the semi elliptical outline of the first order structures along the coastal cordillera may define the location of a characteristic long lived megathrust segment this observation implies a persistence at least over the quaternary of great subduction ruptures along the maule segment

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

integrating 3 d seismic data field analogs and mechanical models in the analysis of segmented normal faults in the wytch farm oil field southern england united kingdom we propose a methodology for the analysis of normal fault geometries in three dimensional 3 d seismic data sets to provide insights into the evolution of segmented normal fault systems and to improve recovery efforts in fault controlled oil fields limited seismic resolution can obscure subtle fault characteristics such as segmentation and gaps in fault continuity that are significant for oil migration and thus accurate reservoir characterization detailed seismic data analyses that incorporate principles of normal fault mechanics however can reveal evidence of fault segmentation we integrate seismic attribute analyses outcrop analog observations and numerical models of fault slip and displacement fields to augment the use of 3 d seismic data for fault interpretation we applied these techniques to the wytch farm oil field in southern england resulting in the recognition of significant lateral and to a lesser extent vertical segmentation of reservoir scale faults slip maxima on fault surfaces indicate two unambiguous segment nucleation depths controlled by the lithological heterogeneity of the faulted section faults initiated preferentially in brittle sandstone and limestone units subsequent growth and linkage of segments predominantly in the lateral direction resulted in composite fault surfaces that have long lateral dimensions and multiple slip maxima reservoir compartmentalization is greatest at the level of prevalent segment linkages which corresponds at wytch farm with the predominant hydrocarbon producing unit the sherwood sandstone at relatively shallower depths fault segments are younger and less evolved resulting in a greater degree of segmentation with intact relay zones

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

large extensional aftershocks in the continental forearc triggered by the 2010 maule earthquake chile summary the mw 8 8 maule earthquake occurred off the coast of central chile on 2010 february 27 and was the sixth largest earthquake to be recorded instrumentally this subduction zone event was followed by thousands of aftershocks both near the plate interface and in the overriding continental crust here we report on a pair of large shallow crustal earthquakes that occurred on 2010 march 11 within 15 min of each other near the town of pichilemu on the coast of the o higgins region of chile field and aerial reconnaissance following the events revealed no distinct surface rupture we infer from geodetic data spanning both events that the ruptures occurred on synthetic sw dipping normal faults the first larger rupture was followed by buried slip on a steeper fault in the hangingwall the fault locations and geometry of the two events are additionally constrained by locations of aftershock seismicity based on the international maule aftershock data set the maximum slip on the main fault is about 3 m and consistent with field results the onshore slip is close to zero near the surface satellite radar data also reveal that significant aseismic afterslip occurred following the two earthquakes coulomb stress modelling indicates that the faults were positively stressed by up to 40 bars as a result of slip on the subduction interface in the preceding megathrust event in other words the pichilemu earthquakes should be considered aftershocks of the maule earthquake the occurrence of these extensional events suggests that regional interseismic compressive stresses are small several recent large shallow crustal earthquakes in the overriding plate following the 2011 mw 9 0 tohoku oki earthquake in japan may be an analogue for the triggering process at pichilemu

w phase source inversion for moderate to large earthquakes 1990 2010 rapid characterization of the earthquake source and of its effects is a growing field of interest until recently it still took several hours to determine the first order attributes of a great earthquake e g m w 7 5 even in a well instrumented region the main limiting factors were data saturation the interference of different phases and the time duration and spatial extent of the source rupture to accelerate centroid moment tensor cmt determinations we have developed a source inversion algorithm based on modelling of the w phase a very long period phase 100 1000 s arriving at the same time as the p wave the purpose of this work is to finely tune and validate the algorithm for large to moderate sized earthquakes using three components of w phase ground motion at teleseismic distances to that end the point source parameters of all m w 6 5 earthquakes that occurred between 1990 and 2010 815 events are determined using federation of digital seismograph networks global seismographic network broad band stations and sts1 global virtual networks of the incorporated research institutions for seismology data management center for each event a preliminary magnitude obtained from w phase amplitudes is used to estimate the initial moment rate function half duration and to define the corner frequencies of the passband filter that will be applied to the waveforms starting from these initial parameters the seismic moment tensor is calculated using a preliminary location as a first approximation of the centroid a full cmt inversion is then conducted for centroid timing and location determination comparisons with harvard and global cmt solutions highlight the robustness of w phase cmt solutions at teleseismic distances the differences in m w rarely exceed 0 2 and the source mechanisms are very similar to one another difficulties arise when a target earthquake is shortly e g within 10 hr preceded by another large earthquake which disturbs the waveforms of the target event to deal with such difficult situations we remove the perturbation caused by earlier disturbing events by subtracting the corresponding synthetics from the data the cmt parameters for the disturbed event can then be retrieved using the residual seismograms we also explore the feasibility of obtaining source parameters of smaller earthquakes in the range 6 0 mw 6 5 results suggest that the w phase inversion can be implemented reliably for the majority of earthquakes of mw 6 or larger