the 2005 and 2010 earthquakes on the sumatra andaman trench evidence for post 2004 megathrust intraplate rejuvenation great earthquakes on oblique subduction zones accommodate slip on strike slip faults on the overriding and subducting plates leading to increased intraplate seismicity after the 2004 sumatra earthquake there was an increase in activity in the wharton basin wb which is considered to be part of a diffuse plate boundary here the intraplate deformation occurs in response to northwest southeast directed compression as opposed to the north northeast south southwest directed plate motion along the sumatra andaman subduction zone earthquakes here mostly occur by left lateral strike slip on north south n s trending fossil fractures although ruptures on east west planes are not uncommon here we discuss the 24 july 2005 m w 7 2 and the 12 june 2010 m w 7 5 earthquakes both of which were left lateral strike slip events sourced in the northern wb our source models for these events based on teleseismic waveform inversion favor slip on the n s fossil fracture systems consistent with previous studies in the wb although the former sourced at similar to 16 km depth was not tsunamigenic the latter similar to 34 km triggered a small tsunami possibly due to its oblique slip at similar to 5 km depth we use conceptual models of plate deformation to suggest that both these events have resulted from post 2004 redistribution of stresses and rejuvenation of intraslab fracture systems within the wb an actively deforming oceanic intraplate region

direct evidence of active deformation in the eastern indian oceanic plate conventional plate tectonics theory postulates that plates only deform on their boundaries to the contrary there is ample evidence of intraplate deformation in the equatorial indian ocean west of the ninetyeast aseismic ridge prior to this study no direct evidence of deforma tion east of the ninetyeast ridge was available we present the results of a multipurpose geo physical cruise showing that intraplate deformation also occurs in this area long at least 1000 km left lateral north south strike slip faults are active and reactivate fossil fracture zones this style of deformation is strikingly different from the east west folds and reverse faults that affect the region west of the ninetyeast ridge contrasting processes of convergence at the northern plate boundaries can account for the two styles of deformation west of the ninetyeast ridge there is a continent continent collision and east of the ridge oceanic lithosphere subducts along the sumatra trench the ninetyeast aseismic ridge therefore appears to be a mechanical border separating two distinct deformed areas

coseismic offsets due to the 11 april 2012 indian ocean earthquakes mw 8 6 and 8 2 derived from gps measurements 1 the 11 april 2012 earthquake mw 8 6 in the indian ocean about 100 km west off the sumatra subduction zone is the largest intraplate strike slip earthquake in the known history two hours later it triggered another great earthquake of mw 8 2 in its vicinity the earthquakes reflect the internal deformation of the diffused plate boundary between india and australia caused by the differential plate motion between them the slip occurred on conjugate planes and the presence of some of them has been reported from the swath bathymetry and satellite magnetic anomalies we estimate coseismic offsets due to these earthquakes at continuous gps sites in the andaman nicobar region and at other international gnss service igs sites around the earthquakes source region the sites on the andaman islands which are about 900 1200 km to the north of the earthquake epicenters experienced predominantly southward coseismic offset of up to 3 cm the nearest site campbell bay on great nicobar island about 500 km to the north of the earthquake documented an ese offset of about 4 cm the coseismic offsets are consistent with the finite fault slip models derived from back projection of the seismic waves recorded by the global networks

mw 8 6 sumatran earthquake of 11 april 2012 rare seaward expression of oblique subduction the magnitude 8 6 and 8 2 earthquakes off northwestern sumatra on 11 april 2012 generated small tsunami waves that were recorded by stations around the indian ocean combining differential travel time modeling of tsunami waves with results from back projection of seismic data reveals a complex source with a significant trench parallel component the oblique plate convergence indicates that 20 50 m of trench parallel displacement could have accumulated since the last megathrust earthquake only part of which has been taken up by the great sumatran fault this suggests that the remaining trench parallel motion was released during the magnitude 8 6 earthquake on 11 april 2012 within the subducting plate the magnitude 8 6 earthquake is interpreted to be a result of oblique subduction as well as a reduction in normal stress due to the occurrence of the sumatra andaman earthquake in 2004

structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation abstract mechanisms responsible for meso and convective scale organization within a large tropical squall line that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment are investigated using a three dimensional numerical cloud model the squall line occurred in an environment typical of fast moving tropical squall lines characterized by moderate convective available potential energy and moderate to strong vertical shear beneath a low level jet with weak reverse vertical shear above a well simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi linear to a three dimensional bow shaped structure over a 2 h period this transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40 60 km long bow shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge within enha

deep seismic reflection images of the wharton basin oceanic crust and uppermost mantle offshore northern sumatra relation with active and past deformation 1 we present deep seismic reflection images along two profiles collected in 2006 in the wharton basin offshore northern sumatra the main profile is located subparallel to the sumatran trench at a distance of 32 66 km faulting of the entire sedimentary section strike slip deformation sometimes accompanied by a dip slip component is imaged over two fracture zones of the extinct wharton spreading center that prior studies have shown to be reactivated as left lateral faults the western fracture zone is associated with a wide region of strong basement topography a difference in crustal thickness of 1 5 km and an age offset of 9 ma the epicenters of the 11 april 2012 mw 8 6 great strike slip earthquake its mw 7 2 foreshock and mw 8 2 aftershock align along this major structure 100 km south of the profile intersection our high quality long offset seismic reflection data also reveal bright dipping reflections extending down to a maximum of 24 km into the oceanic mantle 37 km below sea level apparent dips are mostly 25 35 corresponding to 30 55 along either n s to nne ssw or e w to wnw ese directions which encompass the directions of plate fabric and nodal planes of the mw 8 6 event we suggest that these enigmatic reflections arise from presently inactive dip slip fault planes reaching for the deepest ones to the base of the brittle layer possible origins include extension related to plate bending or an episode of now inactive thrust type deformation reactivating paleonormal faults similar to that taking place in the central indian basin

the 2012 sumatra great earthquake sequence the equatorial indian ocean is a well known place of active intraplate deformation defying the conventional view of rigid plates separated by narrow boundaries where deformation is confined on 11 april 2012 this region was hit in a couple of hours by two of the largest strike slip earthquakes ever recorded moment magnitudes mw 8 6 and 8 2 broadband seismological observations of the mw 8 6 mainshock indicate a large centroid depth 30 km and remarkable rupture complexity detailed study of the surface wave directivity and moment rate functions clearly indicates the partition of the rupture into at least two distinct subevents to account for these observations we developed a procedure to invert for multiple point source parameters the optimum source model at long period consists of two point sources separated by about 209 km with magnitudes mw 8 5 and 8 3 to explain the remaining discrepancies between predicted and observed surface waves we can refine this model by adding directivity along the wnw ese axis however we do not exclude more complicated models to analyze the mw 8 2 aftershock we removed the perturbation due to large surface wave arrivals of the mw 8 6 mainshock by subtracting the corresponding synthetics computed for the two subevent model analysis of the surface wave amplitudes suggests that the mw 8 2 aftershock had a large centroid depth between 30 km and 40 km this major earthquake sequence brings a new perspective to the seismotectonics of the equatorial indian ocean and reveals active deep lithospheric deformation

large intermediate depth earthquakes and the subduction process this study provides an overview of intermediate depth earthquake phenomena placing emphasis on the larger tectonically significant events and exploring the relation of intermediate depth earthquakes to shallower seismicity especially we examine whether intermediate depth events reflect the state of interplate coupling at subduction zones and whether this activity exhibits temporal changes associated with the occurrence of large underthrusting earthquakes historic record of large intraplate earthquakes m b 7 0 in this century shows that the new hebrides and tonga subduction zones have the largest number of large intraplate events regions associated with bends in the subducted lithosphere also have many large events e g altiplano and new ireland we compiled a catalog of focal mechanisms for events that occurred between 1960 and 1984 with m 6 and depth between 40 and 200 km the final catalog includes 335 events with 47 new focal mechanisms and is probably complete for earthquakes with m b 6 5 for events with m 6 5 nearly 48 of the events had no aftershocks and only 15 of the events had more than five aftershocks within one week of the mainshock events with more than ten aftershocks are located in regions associated with bends in the subducted slab focal mechanism solutions for intermediate depth earthquakes with m 6 8 can be grouped into four categories 1 normal fault events 44 and 2 reverse fault events 33 both with a strike nearly parallel to the trench axis 3 normal or reverse fault events with a strike significantly oblique to the trench axis 10 and 4 tear faulting events 13 the focal mechanisms of type 1 events occur mainly along strongly or moderately coupled subduction zones where a down dip extensional stress prevails in a gently dipping plate in contrast along decoupled subduction zones great normal fault earthquakes occur at shallow depths e g the 1977 sumbawa earthquake in indonesia type 2 events with strike subparallel to the subduction zone and most of them with a near vertical tension axis occur mainly in regions that have partially coupled or uncoupled subduction zones and the observed continuous seismicity is deeper than 300 km the increased dip of the downgoing slab associated with weakly coupled subduction zones and the weight of the slab may be responsible for the near vertical tensional stress at intermediate depth and consequently the change in focal mechanism from type 1 to type 2 events events of type 3 occur where the trench axis bends sharply causing horizontal parallel to the trench strike extensional or compressional intraplate stress type 4 are hinge faulting events for strongly coupled zones we observed temporal changes of intermediate depth earthquake activity associated with the occurrence of a large underthrusting event after the occurrence of a large underthrusting event the stress axis orientation of intermediate depth earthquakes changes from down dip tensional to down dip compressional e g 1960 chile 1974 peru 1982 tonga and 1952 kamchatka earthquakes or the number of large intermediate events decreases for a few years e g 1964 alaska and 1985 valparaiso earthquakes we conclude that even though the stress changes induced by slab pull and slab distortion control the general pattern of intermediate depth seismicity spatial and temporal variations of the intraplate stress associated with interplate coupling are important in controlling the global occurrence of large intermediate depth events

aftershocks of the 2012 off coast of sumatra earthquake sequence abstract aftershocks of the 2012 off coast of sumatra earthquake sequence exhibit a complex and diffuse spatial distribution the first order complexity in aftershock distribution is clear and well beyond the influence of typical earthquake location uncertainty the sequence included rupture of multiple fault segments spatially separated we use surface wave based relative centroid locations to examine whether at the small scale the distribution of the aftershocks was influenced by location errors surface wave based relative location has delineated precise oceanic transform fault earthquake locations in multiple regions however the relocated aftershocks off the coast of sumatra seldom align along simple linear trends that are compatible with the corresponding fault strikes as estimated for the gcmt catalog the relocation of roughly 60 moderate earthquake epicentroids suggests that the faulting involved in the 2012 earthquake aftershock sequence included strain release along many short fault segments statistical analysis and temporal variations of aftershocks show a typical decay of the aftershocks but a relatively low number of aftershocks as is common for intraplate oceanic earthquakes coulomb stress calculations indicate that most of the moderate magnitude aftershocks are compatible with stress changes predicted by the large event slip models the patterns in the aftershocks suggest that the formation of the boundary and eventual localization of deformation between the indian and australian plate is a complicated process

slip partitioning along major convergent plate boundaries along plate boundaries characterized by oblique convergence earthquake slip vectors are commonly rotated toward the normal of the trench with respect to predicted plate motion vectors consequently relative plate motion along such convergent margins must be partitioned between displacements along the thrust plate interface and deformation within the forearc and back arc regions the deformation behind the trench may take the form of strike slip motion back arc extension or some combination of both we observe from our analysis of the harvard moment tensor catalog that convergent arcs characterized by back arc spreading specifically the marianas and new hebrides are characterized by a large degree of slip partitioning however the observed rates directions and location of back arc spreading are not sufficient to account for degree of partitioning observed along the respective arcs implying that the oblique component of subduction is also accommodated in part by shearing of the overriding plate in the case of the sumatran arc where partitioning is accommodated by strike slip faulting in the overriding plate the degree of partitioning is similar to that observed along the marianas but the result is viewed with caution because it is based on a predicted plate motion vector that is based on locally derived earthquake slip vectors in the case of the alaskan aleutian arc where back arc spreading is also absent the degree of partitioning is less and rotation of slip vectors toward the trench normal appears to increase linearly as a function of the obliquity of convergence if partitioning in the alaskan aleutian arc is accommodated by strike slip faulting within the upper plate the positive relationship between obliquity of convergence and the rotation of earthquake slip vectors to the trench normal may reflect that either 1 the ratio of the depth extent of strike slip faults behind the trench z s to the subduction thrust z t increases westward along the arc 2 the dip of the subduction thrust increases westward along the arc or 3 the strength of the subduction thrust decreases westward along the arc

back projection imaging of earthquakes back projection analysis of earthquakes is a type of array processing that images the source of seismic waves coherently recorded at stations throughout the seismic network the method was developed following the magnitude 9 2 sumatra andaman earthquake in 2004 although properties of earthquakes have been investigated using array data prior to the introduction of the back projection method this technique differs from other approaches because it makes limited assumptions and allows detailed and complex rupture propagation to be examined these advantages have led several researchers to apply the method to many of the largest earthquakes to occur this century the method has also been effective for the detection of smaller events a critical component of the success of back projection has been the development of large scale dense seismic arrays further improvements and future applications of the method will depend greatly on the continued maintenance and development of these networks

strain partitioning during oblique plate convergence in northern sumatra geodetic and seismologic constraints and numerical modeling global positioning system gps measurements along the subduction zone of northern sumatra 2 s to 3 n reveal that the strain associated with the oblique convergence of the australian plate with eurasia is almost fully partitioned between trench normal contraction within the forearc and trench parallel shear strain within a few tens of kilometers of the sumatran fault kinematic analyses of interplate earthquake slip vectors provide slip rates on the sumatran fault within a few millimeters per year of gps and geologic rates giving us more confidence in the use of slip vectors for inferring slip partitioning elsewhere the inferred slip rate on the sumatran fault is 1 3 less than the full margin parallel component of plate motion an across forearc rotation in the slip vectors suggests that the missing arc parallel shear occurs seaward of the geodetic network between the forearc islands and the trench simple finite element models are used to explore the conditions under which the change in the principal strain rate directions between the forearc and the arc region can occur modeling suggests that neither a preexisting strike slip fault nor a zone of thermally induced lithospheric weakness in the overriding plate is needed for strain partitioning to occur in general forearc slivers form over the region of interplate coupling and are driven along strike by the basal shear a volcanic arc can help the partitioning process by localizing the margin parallel shear strain in the upper plate if its crust and mantle are weaker than its surroundings interplate slip vectors and geodetic results from sumatra together suggest that the highest coupling on the plate boundary occurs beneath and seaward of the forearc islands consistent with inferences about the rupture zones of great nineteenth century earthquakes there the sumatra example suggests that geodetic measurements of interseismic margin parallel shear strain at oblique convergent margins can be used to map the landward extent of the relatively high basal stress beneath the overriding plate if one can correct for strain localization caused by weak upper plate strike slip faults

post deformational annealing at the subgrain scale temperature dependent behaviour revealed by in situ heating experiments on deformed single crystal halite the dynamics of substructures which encompass all structures present at the subgrain scale were investigated by static in situ annealing experiments deformed single crystal halite was annealed

seismic b value anomalies in the sumatran region seismotectonic implications abstract the spatial variations in the seismic b value seismic moment bouguer gravity change and fault plane solution are estimated in the sumatran region based on homogeneous seismicity data from june 2005 to march 2012 to investigate the seismotectonic characteristics and tectonic activity between the 2004 sumatran earthquake and the 2012 east indian ocean earthquakes based on changes in the seismicity rate this time period is divided into five intervals with different earthquake distributions and faulting styles the seismic b values faulting mechanisms and seismic moment release values are mapped throughout the sumatran region and the gravity change every two years between the 2004 event and the 2012 events are determined from satellite grace gravity data the b values vary from 0 45 to 1 59 and an inverse correlation is observed between the b values and convergence rates low b values are located at depths between 20 km and 40 km in the subduction zone and between 20 km and 35 km in the oceanic plate the lowest b values are located at a depth of approximately 28 km in both regions which indicates a homogeneous fault system between them the areas with low b values are associated with megathrust and strike slip mechanisms while the area with the lowest b values is dominated by a megathrust mechanism seismically active regions have low b values associated with a high stress accumulation and high seismic moment release low b value areas are located mainly along the andaman sunda trench and andaman nicobar sumatra forearc temporal variations in the seismicity distribution and faulting style are recognized with temporal variations in the b values in each period relationships exist between the epicenter of the 2004 event and the location of the maximum bouguer gravity change in 2012 and between the epicenters of the 2012 events and the location of the maximum bouguer gravity change in 2004 furthermore a zone of continuous 2 year positive gravity change is located near the nicobar islands the 2004 event boost the 2012 events and intraplate seismicity via stress transfer the seismicity distributions in individual periods within the studied timeframe highlight the active and locked portions of the fault systems

distribution of slip at the northern sumatran fault system we model spatial variations in horizontal displacements of 117 geodetic sites measured during annual surveys in 1989 1996 with the global positioning system gps as elastic strain across a locked strike slip fault to infer the contemporary slip rate locking depth and location of the sumatran fault sf in northern sumatra 1 s 3 n gps derived slip rate estimates increase slightly northward from 23 plus or minus 3 mm yr at 0 8 deg s to 26 plus or minus 2mm yr at 2 7 n they agree with geologic estimates north of the equator but at 0 5 s they are about 10 mm yr higher strain appears to be distributed asymmetrically about the fault south of 2 n about 5 mm yr of shear is required within the offshore forearc west of the fault to achieve a closer agreement of fault locations inferred from gps velocities with geologically identified traces of the sf locking depth estimates are on the order of 10 20 km the western branch of the major fault bifurcation near 1 n slips at a rate five times higher than the eastern branch the two main strands of the fault at the northwestern tip of sumatra 5 5 n appear to be nearly free of horizontal strain significant slip must occur away from the two strands probably further east at two other geologically active branches the banda aceh embayment is extruded to the northwest at a rate of 5 plus or minus 2 mm yr within the estimated velocity uncertainties of several mm yr fault normal deformation along the sf is insignificant almost strain free the northern part of the back arc basin is part of a rigid sunda shelf while the northern forearc is subjected to 8 plus or minus 5 x 10 exp 8 yr of extension nearly parallel to the arc

the 2012 mw 8 6 wharton basin sequence a cascade of great earthquakes generated by near orthogonal young oceanic mantle faults we improve constraints on the slip distribution and geometry of faults involved in the complex multisegment mw 8 6 april 2012 wharton basin earthquake sequence by joint inversion of high rate gps data from the sumatran gps array sugar teleseismic observations source time functions from broadband surface waves and far field static gps displacements this sequence occurred under the indian ocean 400 km offshore sumatra the events are extraordinary for their unprecedented rupture of multiple cross faults deep slip large strike slip magnitude and potential role in the formation of a discrete plate boundary between the indian and australian plates the sugar recorded static displacements of up to 22 cm along with time varying arrivals from the complex faulting which indicate that the majority of moment release was on young wnw trending right lateral faults counter to initial expectations that an old lithospheric nne trending fracture zone played the primary role the new faults are optimally oriented to accommodate the present day stress field not only was the greatest moment released on the younger faults but it was these that sustained very deep slip and high stress drop 20 mpa the rupture may have extended to depths of up to 60 km suggesting that the oceanic lithosphere in the northern wharton basin may be cold and strong enough to sustain brittle failure at such depths alternatively the rupture may have occurred with an alternative weakening mechanism such as thermal runaway

interpretation of sks waves using samples from the subcontinental lithosphere abstract the seismic properties of five south african kimberlite nodules have been calculated from petrofabric measurements these garnet lherzolite and harzburgite composition nodules 56 80 olivine are known from previous studies to have originated at depths of 120 170 km in the subcontinental lithosphere their in situ seismic properties have been calculated by extrapolating the elastic constants to the appropriate temperature 900 1050 c and pressure 3 0 3 5 gpa conditions the average of the five samples has a maximum s wave anisotropy v s of 3 7 which is sufficiently high to explain previously reported teleseismic sks delay times t in continental shield areas of up to 1 7 s the biggest delay time is observed when the foliation is vertical the lineation horizontal and the fastest s wave polarized parallel to the lineation i e an orientation for transcurrent motion delay times of over 1 s can only be generated by this orientation a strong mantle crust mechanical coupling is suggested for such situations the potential use of seismic anisotropy as an indicator of strain in the lithosphere has been investigated using experimental and simulated fabric data for olivine the most abundant phase 70 in the upper mantle the v p and v s seismic anisotropy increases with fabric strength and finite strain recrystallization tends to reduce fabric strength and seismic anisotropy resulting in saturation values for experimental and simulated fabrics which correspond to approximately 50 60 strain or 8 9 v s for pure olivine aggregates a survey of 25 naturally deformed peridotites of oceanic origin suggests an average maximum s wave anisotropy for the olivine component of 9 or about 8 for a lherzolite or harzburgite rock composition when the orthopyroxene component is taken into account the ophiolite samples are twice as anisotropic as the kimberlite nodules if an average anisotropy value is representative of the lithosphere then the sks delay times represent variations in anisotropic layer thickness for delay times over 1 s as the orientation is constrained to be foliation vertical and lineation horizontal the magnitude of s wave anisotropy is less sensitive than v p to variations in olivine volume fraction in range 50 100 and to deformation or fabric intensity further suggesting that s wave anisotropy is particularly apt for the determination of the anisotropic lithosphere thickness for smaller delay times there is some trade off between structural orientation and thickness

tsunami wave analysis and possibility of splay fault rupture during the 2004 indian ocean earthquake the 2004 indian ocean tsunami was observed by two satellites close in space and time that traversed the indian ocean 2 h after the sumatra andaman earthquake but which observed different tsunami lead wave morphologies the earlier satellite jason 1 recorded a lead wave with two peaks of similar amplitude and wavelength while the later satellite topex poseidon recorded a lead wave with only one longer wavelength uplift to resolve this disparity we examine the travel paths of long wavelength waves over the seafloor bathymetry waves traveling from the margin will traverse significantly different paths to arrive at the two satellite transects the result is that the satellites are sensitive to different parts of the margin jason 1 is highly sensitive to the margin in the area of the epicenter while topex is sensitive to a more northerly section by developing solutions of the ocean gravity wave equations accounting for dispersion we show that the double peak of the jason 1 satellite observations are consistent with coseismic rupture of a splay fault of limited along strike extent located north of simeulue island the doubly peaked morphology can be reproduced with co activation of the subduction zone interface and the splay fault which creates a seafloor uplift pattern with two distinct areas of uplift the jason 1 satellite is sensitive to a splay fault in this portion of the margin whereas the topex satellite would not be significantly affected by this uplift pattern by back projecting satellite observation points to the margin we constrain the location of the proposed splay fault and find that it correlates with a bathymetric high the aftershock locations uplift of corals on simeulue island and a fault scarp on pulau salaut besar are also consistent with the activation of a splay fault in the area delimited by the back projection our work also shows that it is critical to fully capture gravity wave dispersion in order to represent features of the lead wave profile that may not be as well characterized by the shallow water long wavelength model it is also necessary to account for dispersion so as to precisely assess wavefront travel times this leads us to conclude that the rupture must have reached very near to the trench and propagated with an updip rupture velocity of order 2 0 km s or more

a numerical study of a squall line over the taiwan strait during tamex iop 2 abstract a two dimensional numerical cloud model was used to investigate a squall line that occurred over the taiwan strait on 16 may 1987 during tamex taiwan area mesoscale experiment this squall line illustrated multicellular behavior as revealed by many doppler analyses the simulated squall line produced 13 new cells successively in a 6 h simulation thus maintaining itself in a long lasting state the simulation result recaptured many of the interesting features also observed the air in the front to rear inflow was ingested into the squall line system primarily from the low levels in front of the system and accelerated upward and backward over a surface pool of cold air in the system relative frame beneath this front to rear flow a rear to front current developed between 2 and 4 km in altitude it descended into the cold pool near the surface part of this descending air moved forward toward the gust front region and part of it moved backward the relative pressure maximum coincided with the co

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

fault interactions and triggering during the 10 january 2012 mw 7 2 sumatra earthquake the 10 january 2012 mw 7 2 sumatra earthquake in the wharton basin occurred 3 months before the great mw 8 6 and mw 8 2 earthquakes in the same region which had complex ruptures and are the largest strike slip earthquakes ever recorded teleseismic p wave back projection of the mw 7 2 earthquake images a unilateral rupture lasting 40 s without observable frequency dependency low frequency 0 05 0 3 hz high frequency 0 3 1 hz in addition to radiation bursts during the mw 7 2 main shock coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about 143 km northeast of the main shock rupture and landward of the trench analysis of globally recorded p waves in both 0 02 0 05 hz velocity records and 1 5 hz stacked envelope functions confirms the presence of coherent sources during the time windows the observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface both dynamic and static triggering could have induced these early aftershocks as they initiated after the surface wave passed by and the coulomb stress perturbations from the mw 7 2 main shock promote earthquakes in the observed locations the earthquake sequence is a clear example of a seaward intraplate strike slip earthquake triggering landward intraplate earthquakes in the same region in contrast to previously reported normal reverse or reverse normal interactions at subduction zones

is the slip rate variation on the great sumatran fault accommodated by fore arc stretching in oblique convergent subduction areas an obliquity increase should produce a slip rate increase on trench parallel strike slip faults and thus the fore arc platelet should be stretched along the great sumatran fault gsf that is associated with the oblique convergent sunda arc a northward increase of the gsf slip rate occurs parallel with the convergence obliquity transpressional back arc deformation accommodates part of the gsf slip rate variation while no significant fore arc stretching is observed the sumatran case shows that oblique convergence may be accommodated by deformation of a 500 km wide zone from the fore arc to the back arc domains

why meter wide dikes at oceanic spreading centers abstract numerical models show that maximum dike width at oceanic spreading centers should scale with axial lithospheric thickness if the pre diking horizontal stress is close to the andersonian normal faulting stress and the stress is fully released in one dike intrusion dikes at slow spreading ridges could be over 5 m wide and maximum dike width should decrease with increasing plate spreading rate however data from ophiolites and tectonic windows into recently active spreading ridges show that mean dike width ranges from 0 5 m to 1 5 m and does not clearly correlate with plate spreading rate dike width is reduced if either the pre diking horizontal stress difference is lower than the faulting stress or the stress is not fully released by a dike partial stress release during a dike intrusion is the more plausible explanation and is also consistent with the fact that dikes intrude in episodes at iceland and afar partial stress release can result from limited magma supply when a crustal magma chamber acts as a closed source during dike intrusions limited magma supply sets the upper limit on the width of dikes and multiple dike intrusions in an episode may be required to fully release the axial lithospheric tectonic stress the observation of dikes that are wider than a few meters such as the recent event in afar indicates that large tectonic stress and large magma supply sometimes exist

dynamical influence of microphysics in tropical squall lines a numerical study abstract based on environmental conditions of the 22 and 23 june squall lines during the convection profonde tropicale in 1981 copt81 experiment in west africa a series of numerical simulations are performed with a two dimensional nonhydrostatic cloud model to examine the dynamical effect of microphysics in tropical squall lines the role of ice phase microphysics strongly depends on ambient conditions for the environment of strong convective instability the ice phase is important regarding the system scale structure but is not important to the convective scale dynamics on the other hand the ice influence is crucial to the squall line convective system if the environment has a weak convective instability and is almost saturated at low levels

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

structural context of the great sumatra andaman islands earthquake 1 a new three dimensional seismic model and relocated regional seismicity are used to illuminate the great sumatra andaman islands earthquake of december 26 2004 the earthquake initiated where the incoming indian plate lithosphere is warmest and the dip of the wadati benioff zone is least steep along the subduction zone extending from the andaman trench to the java trench anomalously high temperatures are observed in the supra slab mantle wedge in the andaman back arc the subducting slab is observed along the entire plate boundary to a depth of at least 200 km these factors contribute to the location of the initiation of rupture the strength of seismic coupling the differential rupture properties between the northern and southern segments of the earthquake and the cause of convergence in the andaman segment

case study of an unusually heavy rain event over eastern taiwan during the mei yu season abstract a heavy rain event during the mei yu season was observed over eastern taiwan on 28 may 2001 under a potentially unstable environment with high cape and copious moisture this event with an unusually high daily rainfall maximum of 307 mm was observed in the ilan area over northeastern taiwan the retrogression of a mei yu front over the nearby ocean collocated with a short wave trough provided favorable large scale conditions for the production of localized heavy rainfall latent heating was suggested to be responsible for the retrogression and the development of the mei yu front over the nearby ocean to the east of taiwan in addition to the large scale forcings the local circulations and local topography modulated the rainfall distribution over the ilan area during the daytime hours the strengthened onshore wind component due to the intensified mei yu frontal circulation and orographic lifting provided enhanced rising motion over the windward slopes of the mountain to produce the significan

implications of the diffuse deformation of the indian ocean lithosphere for slip partitioning of oblique plate convergence in sumatra oblique plate convergence between indian ocean lithosphere and continental crust of the sunda plate is distributed between subduction on the sunda megathrust and upper plate strike slip faulting on the sumatran fault zone in a classic example of slip partitioning over the last decade a destructive series of great earthquakes has brought renewed attention to the mechanical properties of these faults and the intervening forearc crustal block while observations of forearc deformation over the earthquake cycle indicate that the forearc crust is fundamentally elastic the spatial pattern of slip vector azimuths for earthquakes sourced by rupture of the sunda megathrust is strongly inconsistent with relative motion of two rigid plates permanent and distributed deformation therefore occurs in either the downgoing lithospheric slab or the overriding forearc crust previous studies have inferred from geodetic velocities and geological slip rates of the sumatran fault that the forearc crust is undergoing rapid trench parallel stretching using new geological slip rates for the sumatran fault and an updated decadal gps velocity field of sumatra and the forearc islands we instead show that permanent deformation within the forearc sliver is minor and that the sumatran fault is a plate boundary strike slip fault the kinematic data are best explained by diffuse deformation within the oceanic lithosphere of the wharton basin which accommodates convergence between the indian and australian plates and has recently produced several large earthquakes well offshore of sumatra the slip partitioning system in sumatra is fundamentally linked with the mechanical properties of the subducting oceanic lithosphere

evidence of pervasive trans tensional deformation in the northwestern wharton basin in the 2012 earthquakes rupture area abstract the wharton basin in the indian ocean is one of the most extensively deforming ocean basins as confirmed by the occurrence of several very large earthquakes starting from january 12 2012 with mw 7 2 followed by the great earthquakes of april 11 2012 with mw 8 6 and mw 8 2 although the mw 7 2 and mw 8 2 earthquakes seem to have ruptured the re activated n s striking fracture zones the largest event mw 8 6 required the rupturing of several faults oblique to each other in a very complex manner in order to understand the nature of deformation in these earthquakes rupture zones we recently acquired 90 000 km2 of bathymetry 11 400 km of sub bottom profiling gravity and magnetic data covering the rupture areas of the 2012 earthquakes east of the ninety east ridge in the northwestern wharton basin these new data reveal six n8 e striking re activated fracture zones f5b f6a f6b f7a f7b and f8 where the fracture zone f6a can be followed for over 400 km and seems to be most active the epicenters of the mw 8 6 and mw 8 2 earthquakes lie on the fracture zones f6a and f7b respectively the newly observed fracture f5b in the east is short and has an extensional basin at its southern tip the fracture zone f8 defines the eastern boundary of the ninety east ridge the presence of en echelon faults and pull apart basins indicate left lateral motion along these fracture zones in between these fracture zones we observe pervasive 290 striking right lateral shear zones at 4 8 km intervals one of which has cut through a seamount that might have ruptured during the mw 8 6 earthquake we also observe another n20 e striking left lateral shear zones in the vicinity of f7b and f8 which is coincident with the strike of one of the nodal planes of the mw 8 6 focal mechanism these n20 e striking shear zones are interpreted as r riedel shears and the n290 e striking shear zones as r riedel shears these shear zones are formed by a series of n335 e striking en echelon normal faults our data also show the presence of n65 e striking thrust faults east of the ninety east ridge orthogonal to the regional principal direction of compression furthermore extensive bending related faulting is also observed close to the sumatra trench with normal faults also striking at n335 e similar to the normal faults that form the shear zones normal faults with a similar orientation are also present at the southern tip of f5b we explain all these observations with a single coherent model of deformation in the wharton basin where a dominant part of the regional nw se compressional stress is accommodated along the n8 e re activated fracture zones and the rest is distributed along shear zones thrust and normal faults between these fracture zones the thrust and normal faults are orthogonal to each other and define the direction of principal compressive and extensive stresses in the region whereas the two shear zone systems form a conjugate pair

orographic effects on a squall line system over taiwan abstract a north south oriented multicellular squall line during the taiwan area mesoscale experiment s tamex intensive observation period 2 was studied using dual doppler radar data as it moved over the island of taiwan over the open ocean it moved eastward at a constant speed 15 5 m s 1 as the squall line encountered taiwan island s complex mountainous areas the leading edge moved slower in the mountain ridge areas than over the valleys as a result its orientation became approximately parallel to the terrain contours in the upper levels the eastward movement of the squall line aloft was less affected by the terrain compared to the low levels as a result the westward tilt of the rising motion at the front became less significant part of the system relative rear to front flow entered the rising branch of the storm s circulation as a result of orographic lifting as illustrated by the trajectory analysis and was enhanced by latent heat release the system relative rear to front flow did

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

hidden aftershocks of the 2011 mw 9 0 tohoku japan earthquake imaged with the backprojection method 1 the first 25 h of the aftershock sequence following the 11 march 2011 mw 9 0 tohoku japan earthquake is investigated using a backprojection method in total 600 aftershocks are imaged during this time period these aftershocks are distributed over a 500 by 300 km area and include many events in the outer rise the backprojection events are compared with the japan meteorological agency jma catalogue which is composed of earthquakes recorded by local seismic networks in japan surprisingly half of the backprojection events are not found in the jma catalogue these events cluster near the japan trench and in the outer rise and fill in gaps in the spatial distribution of the early aftershock sequence where large main shock slip is thought to have occurred these results show that the jma magnitude of completeness is very high near the trench following the 2011 tohoku main shock and earthquakes as large as magnitude 6 8 went undetected by local seismic networks

explanation of temporal clustering of tsunami sources using the epidemic type aftershock sequence model temporal clustering of tsunami sources is examined in terms of a branching process model it previously was observed that there are more short interevent times between consecutive tsunami sources than expected from a stationary poisson process the epidemic type aftershock sequence etas branching process model is fitted to tsunami catalog events using the earthquake magnitude of the causative event from the centennial and global centroid moment tensor cmt catalogs and tsunami sizes above a completeness level as a mark to indicate that a tsunami was generated the etas parameters are estimated using the maximum likelihood method the interevent distribution associated with the etas model provides a better fit to the data than the poisson model or other temporal clustering models when tsunamigenic conditions magnitude threshold submarine location dip slip mechanism are applied to the global cmt catalog etas parameters are obtained that are consistent with those estimated from the tsunami catalog in particular the dip slip condition appears to result in a near zero magnitude effect for triggered tsunami sources the overall consistency between results from the tsunami catalog and that from the earthquake catalog under tsunamigenic conditions indicates that etas models based on seismicity can provide the structure for understanding patterns of tsunami source occurrence the fractional rate of triggered tsunami sources on a global basis is approximately 14 online material figures of residual analysis for tsunami and earthquake catalogs

the 2 march 2016 wharton basin mw 7 8 earthquake high stress drop north south strike slip rupture in the diffuse oceanic deformation zone between the indian and australian plates the diffuse deformation zone between the indian and australian plates has hosted numerous major and great earthquakes during the seismological record including the 11 april 2012 m w 8 6 event the largest recorded intraplate earthquake on 2 march 2016 an m w 7 8 strike slip faulting earthquake occurred in the northwestern wharton basin in a region bracketed by north south trending fracture zones with no previously recorded large event nearby despite the large magnitude only minor source finiteness is evident in aftershock locations or resolvable from seismic wave processing including high frequency p wave backprojections and love wave directivity analysis our analyses indicate that the event ruptured bilaterally on a north south trending fault over a length of up to 70 km with rupture speed of 2 km s and a total duration of 35 s the estimated stress drop 20 mpa is high comparable to estimates for other large events in this broad intraplate oceanic deformation zone

macrofracturing of oceanic lithosphere in complex large earthquake sequences major earthquakes in oceanic lithosphere seaward of the subduction zone outer trench slope are relatively uncommon but several recent occurrences have involved very complex sequences rupturing multiple nonaligned faults and or having high aftershock productivity with diffuse distribution this includes the 21 december 2010 m w 7 4 ogasawara bonin 11 april 2012 m w 8 6 indo australia 23 january 2018 m w 7 9 off kodiak island and 20 december 2018 m w 7 3 nikol skoye northwest pacific earthquakes major oceanic intraplate event sequences farther from plate boundaries do not tend to be as complex in faulting or aftershocks outer trench slope extensional faulting can involve complex distributed sequences particularly when activated by great megathrust ruptures such as 11 march 2011 m w 9 1 tohoku and 15 november 2006 m w 8 3 kuril islands intense faulting sequences also occur near subduction zone corners with many fault geometries being activated including some in nearby oceanic lithosphere as for the 29 september 2009 m w 8 1 samoa 6 february 2013 m w 8 0 santa cruz islands and 16 november 2000 m w 8 0 new ireland earthquakes the laterally varying plate boundary stresses from heterogeneous locking recent earthquakes or boundary geometry influence the specific faulting geometries activated in nearby major intraplate ruptures in oceanic lithosphere preexisting lithospheric structures and fabrics exert secondary influences on the faulting intraplate stress release in oceanic lithosphere near subduction zones favors distributed macrofracturing of near critical fault systems rather than localized single fault failures both under transient loading induced by plate boundary ruptures and under slow loading by tectonic motions and slab pull

microstructural evolution during initial stages of static recovery and recrystallization new insights from in situ heating experiments combined with electron backscatter diffraction analysis we present in situ observations performed using electron backscatter diffraction of static recovery and recrystallization processes occurring in a plastically deformed geological material namely rocksalt static heating experiments carried out in a scanning electron microscope at temperatures of up to 450 c allowed direct detailed observations of grain boundary migration between substructured grains in deformed polycrystalline samples contrary to expectations crystallographic orientation maps reveal that behind slowly migrating grain boundaries new subgrain boundaries form while pre existing subgrain boundaries are sometimes inherited moreover the crystallographic character especially the preferred orientation of misorientation axes of the new substructures reflects the character of the previous deformation history these results imply that substructural features such as subgrain misorientation distributions may be relatively robust indicators of deformation mechanisms and conditions even in tectonites that have undergone late static recrystallization in addition our observations suggest that the process of static grain boundary migration does not necessarily reset earlier deformation microstructures as commonly assumed the kinematic observations of boundary migrations are inconsistent with simple models in which migration is achieved by single atoms jumping across the boundary

modeling the 2012 wharton basin earthquakes off sumatra complete lithospheric failure a sequence of large strike slip earthquakes occurred west of sunda trench beneath the wharton basin first reports indicate that the main shock was extremely complex involving three to four subevents m w 8 with a maze of aftershocks we investigate slip models of the two largest earthquakes by joint inversion of regional and teleseismic waveform data using the m w 7 2 foreshock we developed hybrid green s functions for the regional stations to approximate the mixture of oceanic and continental paths the main shock fault geometry is defined based on the back projection results point source mechanisms aftershock distribution and fine tune of grid searches the fault system contains three faults labeled f1 89 289 for dip strike f2 74 20 and f3 60 310 the inversion indicates that the main rupture consisted of a cascade of high stress drop asperities up to 30 mpa extending as deep as 50 km the rupture propagated smoothly from one fault to the next f1 f2 and f3 in sequence with rupture velocities of 2 0 2 5 km s the whole process lasted about 200 s and the major moment release 70 took place on the n s oriented f2 the m w 8 2 aftershock happened about 2 h later on a n s oriented fault with a relatively short duration 60 s and also ruptured as deep as 50 km the slip distributions suggest that the earthquake sequence was part of a broad left lateral shear zone between the australian and indian plates and ruptured the whole lithosphere these earthquakes apparently reactivated existing fracture zones and were probably triggered by unclamping of the great sumatran earthquake of 2004

structural evolution and strike slip tectonics off north western sumatra abstract based on new multi channel seismic data swath bathymetry and sediment echosounder data we present a model for the interaction between strike slip faulting and forearc basin evolution off north western sumatra between 2 n and 7 n we examined seismic sequences and sea floor morphology of the simeulue and aceh forearc basins and the adjacent outer arc high we found that strike slip faulting has controlled the forearc basin evolution since the late miocene the mentawai fault zone extends up to the north of simeulue island and was most probably connected farther northwards to the sumatran fault zone until the end of the miocene since then this northern branch jumped westwards initiating the west andaman fault in the aceh area the connection to the mentawai fault zone is a left hand step over in this transpressional setting the tuba ridge developed we found a right lateral strike slip fault running from the conjunction of the west andaman fault and the tuba ridge in ssw direction crossing the outer arc high as a result extrusion formed a marginal basin north of simeulue island which is tilted eastwards by uplift along a thrust fault in the west the shift of strike slip movement in the aceh segment is accompanied by a relocation of the depocenter of the aceh basin to the northwest forming one major neogene unconformity the simeulue basin bears two major neogene unconformities documenting that differences in subsidence evolution along the northern sumatran margin are linked to both forearc evolution related to subduction processes and to deformation along major strike slip faults

tectonic tremor on vancouver island cascadia modulated by the body and surface waves of the mw 8 6 and 8 2 2012 east indian ocean earthquakes author s kundu b ghosh a mendoza m burgmann r gahalaut vk saikia d abstract 2016 american geophysical union all rights reserved the 2012 east indian ocean earthquake mw 8 6 so far the largest intraoceanic plate strike slip event ever recorded modulated tectonic tremors in the cascadia subduction zone the rate of tremor activity near vancouver island increased by about 1 5 times from its background level during the passage of seismic waves of this earthquake in most cases of dynamic modulation large amplitude and long period surface waves stimulate tremors however in this case even the small stress change caused by body waves generated by the 2012 earthquake modulated tremor activity the tremor modulation continued during the passage of the surface waves subsequent to which the tremor activity returned to background rates similar tremor modulation is observed during the passage of the teleseismic waves from the mw 8 2 event which occurs about 2 h later near the mw 8 6 event we show that dynamic stresses from back to back large teleseismic events can strongly influence tremor sources

temperature dependent grain boundary migration in deformed then annealed material observations from experimentally deformed synthetic rocksalt abstract grain boundary migration between strained substructured grains and newly appearing strain free grains has been observed during static in situ annealing of pre deformed rocksalt in the sem with increasing temperature t the migration velocity increases and the character of grain boundary migration changes as temperature increases there is an increase in the length of individual migrating boundary segments that move at similar rates in addition the frequency of migrating boundaries that form traces of a 100 boundary plane of at least one of the crystals involved increases and moving grain boundaries between new and old grains change from highly irregular to smooth straight boundaries at the same time there is a decrease in the influence of the substructure of pre existing strained grains on the grain boundary movement resultant microstructures reflect these changes at 325 350 c the deformed then annealed microstructure is characterized by very irregular grain boundaries a high abundance of 5 50 m scale remnants of old substructured grains within new grains giving a poikilitic microstructure at 350 400 c grain boundaries often exhibit elongate embayments into the strained grains and most remnants of old strained grains are located at former grain boundaries at 400 c grain boundaries between new and old strained grains are straight to smoothly curved the grain boundary velocity observations are explained by the effect of temperature on mobility coupled with local driving force variations additionally at low annealing temperature impurity solute drag and driving force variations are influential while at high temperature the anisotropy in grain boundary energy with crystallographic orientation becomes more important transferring the knowledge from our experiments to geological samples enables us to recognize and interpret similar microstructures in rocks thereby making it is possible to relate microstructural characteristics to the pre annealing and post deformational annealing history

segmentation of the sumatran fault segmentation of the sumatran fault is discerned using an analytical approach in which a k means algorithm partitions earthquakes into clusters of seismicity along the fault clusters are tessellated into segment zones from which segment lengths and maximum credible magnitude are estimated decreasing the depth of seismicity sampled from 70 to 60 to 50 km reduces interaction with deeper seismicity and results from the k means algorithm initially suggest that the fault has k 14 16 and 16 clusters respectively after inspection it becomes clear that the optimum number of clusters is 16 the 16 cluster model developed into zones generates segment lengths ranging from 22 to 196 km and maximum earthquake potentials in the range of mw 6 5 7 8 the sumatran fault is dominated by eight great central segments distributed approximately symmetrically about lake maninjau these central fault segments dominate the hazard which is less in the far north because segments are shorter

the march 11 2011 tohoku oki earthquake and cascading failure of the plate interface 1 a continuous back projection analysis using data recorded in north america between march 9 2011 and april 7 2011 is applied to the mw 9 0 2011 tohoku oki earthquake and the foreshocks and aftershocks of this event as with the mw 8 8 2010 maule chile earthquake back projection results of the mainshock show variations in rupture behavior when data filtered to different frequency ranges are used in particular there is a relationship between the frequency of data used and the position along the dip direction of the energy release with the highest frequency result imaging energy at the down dip edge of the rupture and progressively lower frequencies showing a continuous shift updip in addition these results show that late in the rupture 200 seconds after the hypocentral time energy at all frequencies is imaged very close to the trench at about 37 n which with the energy imaged near and updip of the epicenter may have acted as a tsunami source comparing the mainshock rupture area to the area that ruptured during m 6 foreshocks and aftershocks between march 9th and april 7th shows that total failure of the plate interface nearly doubled compared to the mainshock alone building upon the idea that the mainshock occurred through interactions between multiple segments the results imply that the total failure area of the interface may represent the area that can rupture during a single event as a series of in phase interface segments

triggered aseismic slip adjacent to the 6 february 2013 mw 8 0 santa cruz islands megathrust earthquake abstract aseismic or slow slip events have been observed in many subduction zones but whether they affect the occurrence of earthquakes or result from stress changes caused by nearby events is unclear in an area lacking direct geodetic observations inferences can be made from seismological studies of co seismic slip associated stress changes and the spatiotemporal nature of aftershocks these observations indicate that the february 2013 mw 8 0 santa cruz islands earthquake may have triggered slow or aseismic slip on an adjacent section of the subduction thrust over the following hours to days this aseismic event was equivalent to mw 7 6 significantly larger than any earthquakes in the aftershock sequence the aseismic slip was situated within the seismogenic portion of the subduction interface and must have occurred to the south of the main seismic slip and most aftershocks in order to promote right lateral faulting in the upper plate the dominant deformation style of the aftershock sequence this plate boundary segment can support either stable sliding aseismic or stick slip seismic deformation in response to different driving conditions the complete lack of aftershocks on the thrust interface implies this pair of megathrust slip episodes seismic and aseismic released a substantial portion of the stored strain on the northernmost section of the vanuatu subduction zone

a submarine landslide source for the devastating 1964 chenega tsunami southern alaska abstract during the 1964 great alaska earthquake m w 9 2 several fjords straits and bays throughout southern alaska experienced significant tsunami runup of localized but unexplained origin dangerous passage is a glacimarine fjord in western prince william sound which experienced a tsunami that devastated the village of chenega where 23 of 75 inhabitants were lost the highest relative loss of any community during the earthquake previous studies suggested the source of the devastating tsunami was either from a local submarine landslide of unknown origin or from coseismic tectonic displacement here we present new observations from high resolution multibeam bathymetry and seismic reflection surveys conducted in the waters adjacent to the village of chenega the seabed morphology and substrate architecture reveal a large submarine landslide complex in water depths of 120 360 m analysis of bathymetric change between 1957 and 2014 indicates the upper 20 50 m 0 7 km3 of glacimarine sediment was destabilized and evacuated from the steep face of a submerged moraine and an adjacent 21 km2 perched sedimentary basin once mobilized landslide debris poured over the steep 130 m high face of a deeper moraine and then blanketed the terminal basin 465 m water depth in 11 5 m of sediment these results combined with inverse tsunami travel time modeling suggest that earthquake triggered submarine landslides generated the tsunami that struck the village of chenega roughly 4 min after shaking began unlike other tsunamigenic landslides observed in and around prince william sound in 1964 the failures in dangerous passage are not linked to an active submarine delta the requisite environmental conditions needed to generate large submarine landslides in glacimarine fjords around the world may be more common than previously thought

the 2012 mw 8 6 indian ocean earthquake deep nucleation on a listric like fault abstract the 2012 mw 8 6 indian ocean earthquake the largest instrumentally recorded strike slip event has been described as a westward rupture on orthogonal faults that are part of the original oceanic fabric of the region reported estimates of its depth vary from 10 to 45 km while the maximum depth of its inferred rupture extends to 50 60 km the complexity of the earthquake is undeniable both in terms of fault geometry and rupture propagation with debates on the geometry of the causative faults results from recent seismic surveys enable a fresh look at the earthquake fault geometry nucleation depths and lithospheric rheology in the present study these new findings are incorporated into 22 forward models using a revised velocity structure and n s geometries that flatten with depth the rupture initiation is modeled in the uppermost mantle 25 30 km as well as in the upper mantle at 45 km the latter of which is 15 20 km below the commonly accepted values of maximum depth for frictional failure our study shows that the westward directionality of wave propagation is achieved for strike slip failure on a listric like fault in contrast to subvertical geometries as previously suggested this propagation is persistent for a strike slip failure only for events nucleating at upper mantle depths 45 km rather than for those set to originate at depths between 25 and 30 km however for a dip slip failure the westward propagation is found to be consistent at both nucleation depths on a listric like fault this study highlights a deep nucleation within the lithospheric mantle for the 2012 mw 8 6 earthquake that could be due to strain localization induced by fluid rock interaction and or mineral transformation crystallization near the 680 c isotherm at 45 km depth 1 4 gpa which correlates with deep serpentinization on faults

intermediate term seismic precursors for some coupled subduction zones the paper discusses model results and then reviews observational data concerning some aspects of the mechanics of mature seismic gaps in coupled subduction zones the concern is with space and time varying stresses as signalled by the presence and mechanisms of earthquakes in the outer rise zones adjacent to main thrust areas of large subduction events and down dip from such areas in the downgoing slab observations are shown to be consistent with the expectation that in mature seismic gaps as a result of interplate boundary locking in presence of sustained gravitational driving forces at least the deeper portions of the ocean plate in the outer rise zones are under increased compression and the downgoing slab is under increased tension the observational data cover two cases of closed seismic gaps namely the region of the chilean valparaiso earthquake of march 3 1985 and the earthquake of october 4 1983 four other cases concern still to be closed gaps in northern chile and along the coast of guatemala and also the kurile islands trench gap and the northern new hebrides gap it is concluded that the intermediate term precursor consisting of a combination of compressional outer rise earthquake s and tensional intermediate depth intra plate events in the downgoing slab which mechanically signals the latter part of the earthquake cycle could be useful in evaluating the maturity and hence great earthquake potential of a seismic gap

seismic stratigraphy and subsidence evolution of the northwest sumatra fore arc basin abstract new seismic reflection data collected with the indonesian rv baruna jaya iii under a french indonesian cooperative program allowed to study the geodynamic evolution and the seismic stratigraphy off northern sumatra within the sumatra fore arc domain the direction of subduction of the indian oceanic crust below the sunda arc is normal in front of java and oblique along sumatra as a result parts of the sumatra margin are moving northwards along two large strike slip faults parallel to the subduction trench the sumatra fault in sumatra and the mentawai fault at sea which separates the accretionary prism from the fore arc basin we describe the relationships between the seismic stratigraphy and the sedimentary history and we propose a tectonic evolution of the fore arc domain after widespread uplift and erosion during the paleogene the fore arc basin becomes subsident during the miocene as evidenced by shelf deposits organized in two transgressive regressive sequences 2a 2b produced by tectonics and eustatism this is interpreted as the result of a limited e w extension linked to the incipient play of the sumatra and mentawai faults in pliocene quaternary times the fore arc basin is segmented into several sub basins aceh simeulue and nias basins by compressional zones or by strike slip faults the subsidence rate increased strongly producing sequence 3 with two or four subunits for the pliocene and sequence 4 for the quaternary during this period local variations of the sediments thickness and of the number of sequences indicate that tectonics prevails over eustatism in the fore arc basin the sumatra margin is one of the best examples in the world to study the relationships between sedimentary and tectonic processes in an oblique subduction zone

the april 2012 indian ocean earthquakes seismotectonic context and implications for their mechanisms the 11 april 2012 earthquakes m w 8 6 and m w 8 2 were sourced within the northern wharton basin in the northeastern part of the indo australian diffuse plate boundary this unusually active oceanic intraplate region has generated many large earthquakes in the past most of which are believed to have occurred by strike slip motion triggered by the nw se oriented compressional stresses acting across the indian and australian plates in the aftermath of the 2004 megathrust earthquake along the nearby sunda trench increased seismicity in the northern wharton basin is attributed to the stress transfer from the sumatra andaman plate boundary models proposed for the april 2012 earthquakes differ somewhat in details but partly attribute their complex rupture to the reactivation of pre existing structures these structures include previously mapped n s trending fracture zones within the northern wharton basin and e w lineations across the ninetyeast ridge in this paper we review the regional tectonics and past seismicity on the indo australian plate in order to understand the seismotectonic setting of the april 2012 indian ocean earthquakes c 2014 elsevier b v all rights reserved