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LITHOS-CAPP is the German contribution to the international ScanArray experiment. ScanArray is an array of broadband seismometers with which we aim to study the lithosphere and upper mantle beneath the Scandinavian Mountains and the Baltic Shield. LITHOS-CAPP contributed 20 broadband recording stations from September 2014 to October 2016, 10 in Sweden and 10 in Finland, continuously recordings at 100 samples per second. The stations were deployed by the KIT Geophysical Institute and GFZ section 2.4 (seismology). They form part of the temporary network ScanArrayCore (FDSN network code 1G 2012-2017). This data publication contains the original log-files of the recorders.

The SWATH-D experiment is dense deployment of 154 seismic stations in the Central and Eastern Alps between Italy and Austria, complementing the larger-scale sparser AlpArray Seismic Network (AASN). SWATH-D will provide high resolution images from the surface into the upper mantle, and allow observations of local seismicity. SWATH-D focuses on a key area of the Alps where the hypothesized flip in subduction polarity has been suggested, and where an earlier seismic profile (TRANSALP) has imaged a jump in the Moho. Where mains power is available (at ca. 80 sites) stations are providing realtime data via the cellphone network and are equipped with Güralp CMG-3EPSC (60s) seismometers and Earth Data Recorders EDR-210. The rest of the stations are offline and consist mainly of Nanometrics Trillium Compact (120s) and Güralp CMG-3EPSC (60s) seismometers equipped with either Omnirecs CUBE3 or PR6-24 Earth Data Loggers. All stations are equipped with external GPS antennas and the sampling rate is 100 Hz (Heit, et al., 2018). The network will operate for 2 years starting in July 2017. The Swath-D data will be used directly by 20 individual proposals of the MB-4D Priority Program (Mountain Building Processes in Four Dimensions, 2017) of the German Research Foundation (DFG) and data products derived from it will contribute to additional 13 proposals. SWATH-D is thus an important link between the MB-4D Priority Program and the international AlpArray communities and a scientific service to many of the proposals within the DFG Priority Program. Waveform data are available from the GEOFON data centre, under network code ZS, and are embargoed until August 2023. After the end of embargo, data will be openly available under CC-BY 4.0 license according to GIPP-rules.

Hundreds of submarine communication cables cross the world's oceans. Today, these cables are unaware of their environment. However, repeaters spaced at ~50 km intervals along them offer access to power and bandwidth, providing the opportunity to add sensor capability to future SMART cables (Science Monitoring And Reliable Telecommunications), a concept advanced by a Joint Task Force of the International Telecommunication Union, the World Meteorological Organization and the Intergovernmental Oceanographic Commission of UNESCO1. Two NASA workshops focused on applications in climate research and oceanography2. In the workshop described here, research scientists, practitioners from earthquake observatories and tsunami warning centers, and engineers discussed potential applications of SMART cables for earthquake and tsunami early warning and reviewed existing approaches and how they can benefit from SMART cables. They also considered what possibilities exist in research on Earth structure, the physics of earthquakes, and tsunami excitation and propagation. According to current planning, a first generation of SMART cables will be equipped with a simple instrumentation package containing accelerometers, pressure gauges and temperature sensors in order to make the sensor package simple and able to withstand the rough deployment conditions in standard cable-laying operations. Most destructive tsunamis are triggered by great earthquakes along the plate boundary faults in subduction zones. Their offshore location makes quick detection and assessment of their tsunamigenic potential a real challenge using land-based networks. The DART system of ocean bottom pressure detectors can detect ocean-crossing tsunamis but sensors are too sparse and too far from shore to be much help in local warning. Dedicated submarine cables present another real-time solution but come with a hefty price tag. Thus a comprehensive coverage of all endangered subduction zones is out of reach, particularly in the developing world. Already a few cables crossing the Pacific can reduce the time-to-detection of potentially tsunamigenic earthquakes along the Ring of Fire by ~20%, and the detection of the actual tsunami wave would be reduced by a similar fraction. With trench-parallel cables even larger improvements are possible. The continuous high sampling rates possible in a cable allow separation of tsunami and seismic wavefields, allowing reliable tsunami measurements in the near field. Wide science benefits are expected from the faithful recordings of offshore earthquakes as well as from the vastly improved coverage of the ocean basins from even a small number of SMART cables.

International audience; The Precambrian rocks of Madagascar were formed and/or modified during continental collision known as the Pan-African orogeny. Aborted Permo-Triassic Karoo rifting and the subsequent separation from Africa and India resulted in the formation of sedimentary basins in the west and volcanic activity predominantly along the margins. Many geological studies have documented the imprint of these processes, but little was known about the deeper structure. We therefore deployed seismic stations along an SE-NW trending profile spanning nearly all geological domains of southern Madagascar. Here we focus on the crustal structure, which we determined based on joint analysis of receiver functions and surface waves derived from ambient noise measurements. For the sedimentary basin we document a thinning of the underlying crystalline basement by up to ∼60% to 13 km. The crustal velocity structure demonstrates that the thinning was accomplished by removal or exhumation of the lower crust. Both the Proterozoic and Archean crust have a 10 km thick upper crust and 10–12 km thick midcrust. However, in contrast to the typical structure of Proterozoic and Archean aged crust, the Archean lower crust is thicker and faster than the Proterozoic one, indicating possible magmatic intrusions; an underplated layer of 2–8 km thickness is present only below the Archean crust. The Proterozoic mafic lower crust might have been lost during continental collision by delamination or subduction or thinned as a result of extensional collapse. Finally, the Cretaceous volcanics along the east coast are characterized by thin crust (30 km) and very large V P ∕V S ratios.

We have inferred the Vp/Vs ratio along the segment of the Peru-Chile subduction margin corresponding to the rupture area of the Tocopilla earthquake (Mw 7.7, 14/11/2007). This event nucleated in Northern Chile and broke the southern ~100 km of the ~500 km Northern Chile Southern Peru seismic gap, which at the time had not seen an earthquake of this magnitude since the M~9 event of 1877. Tocopilla event activated two main co-seismic slip patches: one around the epicenter and another north-east of the Mejillones Peninsula. We have applied the Lin and Shearer (2007) approach to the aftershock sequence of the Tocopilla event. In this approach, the relative time shift between the S phases of a pair of nearby events at one station are plotted as function of the time shifts between the P phases of the same pair. The process is repeated for a cluster of events. If the events are close enough to assume a locally uniform Vp/Vs ratio and the P-reciprocal wavefront can be approximated as planar, the points lay on a line, whose slope is an estimation of the local Vp/Vs. The technique is extended to a set of stations demeaning the time shifts from each pair of events. The time shifts are inferred maximizing the cross-correlation function between the event pairs. The technique has been applied to clusters of events sharing similar waveforms and spatially clustered hypocentres. We have adopted a robust linear regression and have assigned a statistical error to the best fit. Clusters have been identified along the whole profile of the subducting slab, although most clusters falls within a sub-vertical branch of the subduction interface hosting a major aftershock (Michilla earthquake, 16/12/2007, Ml 6.8) and its aftershocks. This branch falls inside the subducted Nazca Plate at depths of 40-50 km, north-east of the Mejillones Peninsula, and shows Vp/Vs mostly in the range 1.7-1.8. Clusters of the plate interface shallower than about 30 km show Vp/Vs around 1.9, while at intermediate depths (30-40 km) Vp/Vs is ~1.8. We speculate on the existence of hydrated crust producing the highest Vp/Vs (~1.9 or larger) observed at shallow depths.

We have inferred the Vp/Vs ratio along the segment of the Peru-Chile subduction margin corresponding to the rupture area of the Tocopilla earthquake (TE, Mw 7.7, 14/11/2007). This event nucleated in Northern Chile and broke the southern ~100 km of the ~500 km Northern Chile Southern Peru seismic gap, which had not seen an earthquake of this magnitude since the M~9 event of 1877. TE activated two main co-seismic slip patches: one around the epicenter and another north-east of the Mejillones Peninsula. We have applied the Lin and Shearer approach [1] to the aftershock sequence of TE. In this approach, the relative time shift between the S phases of a pair of nearby events at one station are plotted as function of the time shift between the P phases of the same pair. The process is repeated for a set of events. If the events are close enough to assume a uniform local Vp/Vs and the P-reciprocal wavefront can be approximated as planar, the points lay on a line, whose slope is an estimation of the local Vp/Vs. The technique is extended to a set of stations demeaning the time shifts from each pair of events. The time shifts are inferred maximizing the cross-correlation function between the event pairs. The technique has been applied to clusters of events sharing similar waveforms and spatially clustered hypocentres. We have adopted a robust linear L2 regression and have assigned a statistical error to the best fit. Most clusters are identified within a sub-vertical branch of the subduction interface hosting a major aftershock (Michilla earthquake, 16/12/2007, Ml 6.8) and its aftershocks. This branch falls inside the subducted Nazca Plate at depths of 40-50 km, north-east of the Mejillones Peninsula, and shows Vp/Vs mostly in the range 1.8-1.9. Clusters close to the Mejillones Peninsula and to the epicenter displays Vp/Vs around 1.7 and 1.8, respectively. References [1] - Lin, G., & Shearer, P. (2007). Estimating local Vp/Vs ratios within similar earthquake clusters. Bulletin of the Seismological Society of America, 97 (2), 379-388.

The Maule earthquake (2010 February 27, Mw 8.8, Chile) broke the subduction megathrust along a previously locked segment. Based on an international aftershock deployment, catalogues of precisely located aftershocks have become available. Using 23 well-located aftershocks, we calibrate the classic teleseismic backprojection procedure to map the high-frequency seismic radiation emitted during the earthquake. The calibration corrects traveltimes in a standard earth model both with a static term specific to each station, and a ‘dynamic’ term specific to each combination of grid point and station. The second term has been interpolated over the whole slipping area by kriging, and is about an order of magnitude smaller than the static term. This procedure ensures that the teleseismic images of rupture development are properly located with respect to aftershocks recorded with local networks and does not depend on accurate hypocentre location of the main shock. We track a bilateral rupture propagation lasting ∼160 s, with its dominant branch rupturing northeastwards at about 3 km s−1. The area of maximum energy emission is offset from the maximum coseismic slip but matches the zone where most plate interface aftershocks occur. Along dip, energy is preferentially released from two disconnected interface belts, and a distinct jump from the shallower belt to the deeper one is visible after about 20 s from the onset. However, both belts keep on being active until the end of the rupture. These belts approximately match the position of the interface aftershocks, which are split into two clusters of events at different depths, thus suggesting the existence of a repeated transition from stick-slip to creeping frictional regime.

Northern Chile has recently been struck by the Mw 8.1 Pisagua earthquake, which occurred on 01/04/2014 and partially filled the Iquique seismic gap. The Pisagua earthquake has been preceded by intense foreshock activity which started in July 2013 and culminated in a cluster of events in March 2014. We have inferred the rupture dynamics of the mainshock and of its largest (Iquique) aftershock (03/04/2014, Mw 7.6) by backprojecting the high-frequency seismic radiation released during the events and recorded by 310 stations of USArray. The time-evolution of the high-frequency (1-4 Hz) energy radiated during the mainshock shows that the rupture lasted about 80 s, with most of the energy released between 25 s and 50 s from the onset. The cumulative energy emitted during the whole rupture process mainly originated downdip the epicenter just off the coast line, approximately in the latitude range 19.5°-20°S. This region falls at the down-dip side of the co-seismic slip area, similarly to the case of the Maule earthquake (South Chile, 27/02/2010, Mw 8.8) and of other large earthquakes. Differently from the Maule case, most aftershocks not located in the area of large seismic radiation. The time-evolution of the coherent seismic radiation displays an initial low-energy phase (lasting about 20s) during which the source starts to migrate from the nucleation point at the epicenter towards the south-east, activating deeper parts of the subduction interface. After reaching points close to the coast line (after ~30s from the onset), the source moves back towards the epicenter mainly activating in sequence two patches of the interface located around 20°S,70.5°W (F1) and 19.7°S,70.2°W (F2), shortly followed by the activation of points close to the area of the largest co-seismic slip (F3). In the last ~15s of the fracturing (F4), the re-activation of the area releasing energy during F2 is observed. Thus, despite the simple bullseye co-seismic slip pattern, the history of energy radiation is quite scattered, suggesting peculiar and sharply site-dependent frictional properties along this segment of the Chilean subduction interface. The Mw7.6 aftershock displays a similar time-evolution of the radiating source, with an initial low-energy stage, during which the rupture front migrates from the epicenter towards deeper zones. Most energy is released about 25s from the onset, when the rupture front reaches points around 20.5°S,70.0°W.

Seismology is often associated with the investigation of earthquake processes and indeed this is a very important target of the science. However, seismology is also the primary means by which we can obtain images of the internal structure of the Earth on all scales, ranging from the deep interior, i.e. the Earth’s core and lower mantle over the mantle lithosphere and crust, the scale at which plate tectonics ‘happens’ all the way to the unconsolidated material in the near-surface. Seismology uses earthquakes and artificial sources as signal generators but also the ambient background wavefield, previously considered to be merely noise. Methodological and instrumental innovations have allowed ever more detailed investigations of the earthquake process and the seismic structure, and opened up new targets such as as the monitoring of geomorphological events and investigations of the time-dependency of seismic structure. Finally seismology is not restricted to waveform analysis and the instrumental period but draws on historical data and, in the field of paleoseismology, geological markers to constrain seismic activity in the pre-instrumental past. Direct societal benefits from seismology accrue for example from improved seismic hazard estimates and early-warning technologies in the area of natural hazards, from improved recovery and usage of natural resources, including geothermal energy as a sustainable energy source and much more, e.g. the possibility to monitor and thus enforce compliance with the nuclear test ban treaty.

Madagascar occupies a key position in the assembly and breakup of the supercontinent Gondwana. It has been used in numerous geological studies to reconstruct its original position within Gondwana and to derive plate kinematics. Seismological observations in Madagascar to date have been sparse. Using a temporary, dense seismic profile across southern Madagascar, we present the first published study of seismic anisotropy from shear wave splitting analyses of teleseismic phases. The splitting parameters obtained show significant small-scale variation of fast polarization directions and delay times across the profile, with fast polarization rotating from NW in the center to NE in the east and west of the profile. The delay times range between 0.4 and 1.5 s. A joint inversion of waveforms at each station is applied to derive hypothetical one-layer splitting parameters. We use finite-difference, full-waveform modeling to test several hypotheses about the origin and extent of seismic anisotropy. Our observations can be explained by asthenospheric anisotropy with a fast polarization direction of 50°, approximately parallel to the absolute plate motion direction, in combination with blocks of crustal anisotropy. Predictions of seismic anisotropy as inferred from global mantle flow models or global anisotropic surface wave tomography are not in agreement with the observations. Small-scale variations of splitting parameters require significant crustal anisotropy. Considering the complex geology of Madagascar, we interpret the change in fast-axis directions as a ~150 km wide zone of ductile deformation in the crust as a result of the intense reworking of lithospheric material during the Pan-African orogeny. This fossil anisotropic pattern is underlain by asthenospheric anisotropy induced by plate motion.

In news reports we are accustomed to see earthquakes symbolised with a dot or star on a map and associated with a magnitude, the bigger the scarier. For at least moderately sized earthquakes seismologists additionally have been routinely determining the type of rupture just from observing the pattern of radiated seismic energy. In reality earthquakes do not occur as a point but rupture a fault plane. For small earthquakes this distinction can be neglected but for the largest earthquakes the rupture plane can extend for hundreds of kilometres, and the actual rupture propagation begins to have a strong influence on the hazard that the earthquake presents – whether the rupture proceeds to the north or the south and how deep and shallow it reaches determines which cities will be hit the hardest, whether shaking is moderate or intense, and whether a sizeable tsunami is triggered. The explosion of the availability of ground-, ocean- and space-based observation technologies in the last decade has allowed seismologists to map the rupture process in unprecedented detail even for challenging subduction zone earthquakes. The same technology can be used to observe potential precursory processes and the postseismic relaxation by which the earth regains its equilibrium following the disturbance that a great earthquake represents. Focussing on the Mw 8.1 Iquique earthquake in northern Chile on April 1, 2014, we will discuss the state-of-the-art in monitoring great earthquakes and their aftermath.

We back-project the seismic radiation released by Maule earthquake (Chile, 27/02/2010, Mw 8.8) in three frequency bands: 0.4-3 Hz, 1-4 Hz, 2-8 Hz. We measure the coherence of the seismic traces at 557 stations of US array by semblance. Travel times are estimated starting from a 1D global velocity model (ak135) corrected by two terms: a static correction and a dynamic correction. Static corrections are the mean time corrections to the 1D velocity model, and dynamic corrections are finer time shifts depending on the source-receiver path. Both terms are extracted from the time shifts between different receivers of P-phases of 23 high-magnitude calibration aftershocks, most of which have high precision locations based on the temporary deployment following the Maule earthquake (IMAD). The dynamic corrections are extended over a fine source grid by kriging interpolation. This procedure makes the backprojection results independent of the main shock catalog hypocentre and allows coherent imaging to higher frequencies. During the first 20 seconds of the rupture process, the source is stable nearby the nucleation point, which is close to epicentre proposed by Vigny et al (Science, 2011) based on high rate GPS motion. Afterwards, it moves bilaterally, with the northern front moving with an average velocity of ∼3 km/s. Most of the energy is emitted from the northern patch of the bi-lateral rupture (∼70%), with sporadic emissions from the southern patch. The maximum of stacked energy is located about 150 km north-eastwards from the epicenter and a relative maximum appears south of Arauco peninsula. In the dip direction, energy is mostly emitted from the down-dip edge of the co-seismic area, roughly matching the aftershock distribution. Specifically, we find that coherent radiation is emitted from two distinct belts nearly parallel to the trench. The position of these belts is in good agreement with the location of the aftershocks, which also are arranged in two disconnected zones of the subduction interface at different depths, the deeper of which is characterised by a large number of repeating event clusters (Rietbrock, Jenkins et al., this session). Thus, our backprojection analysis in combination with the aftershock distribution demonstrates the existence of a peculiar doubled downdip transition from seismogenic behaviour to stable sliding. We suspect fluids released from the downgoing plate to be the cause of the transitions in frictional behaviour because of (1) the co-location of high Vp/Vs ratios with the deep interface seismicity, (2) systematic decrease of depth of onset of deeper seismicity with younging incoming plate age, (3) patchy occurrence along-strike of deeper seismicity.

We investigate repeating earthquakes (REs) on the Chile subduction zone, in the first 9 months following the Maule 2010 M 8.8 earthquake. Using the aftershock catalogue of approximately 30,000 events (Rietbrock et al., 2012) and the data from the International Maule Aftershock Dataset (IMAD), we identify 1550 clusters of small magnitude (Mw ~1.5-3) events showing similar waveforms (cross-correlation coefficients>0.9). Clusters are found from the surface to depths of ~60km, indicating the generation of RE on pre-existing crustal faults and slab interface. A particularly dense band of clustered seismicity runs NE-SW along the length of Chile at 37-47km depth on the slab/continent interface, apparently defining the limit of plate coupling (Rietbrock et al, 2012; Lange et al., 2012). Relocation of deep clusters, via the double difference method (hypoDD), reveal that they lie within a region of increased fluid content (interpreted from high Vp/Vs ratio (Hicks et al., 2012)), and define streaks of seismicity orientated down-dip. Moment tensor analysis of selected aftershocks shows that larger events M 4-5 are located at the interface or deeper in the slab (5-8km beneath the slab interface) and show thrust motion along the direction of the plate interface. REs, in contrast, show predominantly strike-slip motion and are located close to the interface. Temporal analysis also shows non-constant recurrence times of events within clusters, which we interpret as an indication that the seismicity in the deep clusters are driven by pulses of after-slip from the Maule 2010 event together with episodic fluid migration. We introduce a model of Mixed Mode Fault Slip (MMFS) to explain our observations, where aseismic sliding of trench sediments in the subduction channel build up stress on fragments of ocean crust, causing them to repeatedly fracture and generate repeating earthquakes.

Using direct shear waves in addition to SKS waves for splitting measurement would be advantageous in splitting measurements since they sample possible anisotropic structures in the upper mantle with an increased range of incidence angles and back azimuths. However, source-side contamination of direct S-waves makes splitting measurements complicated although all shear waves theoretically suitable for splitting analyses as long as the angle of incidence at surface is smaller than 35_. Here we introduce the reference station technique, a direct S wave-based method in the estimation of shear-wave splitting parameters. The method depends on maximizing the correlation between seismic traces with direct-S wave signal at reference and target stations of a station pair after correcting the reference station for the receiver side anisotropy effect using SKS splitting parameters. The procedure effectively assumes the same source side anisotropy affecting the two stations for the same seismic event. Only a few stations with well-constrained SKS splitting results are needed as seeds to determine the splitting parameters of a large array in an iterative manner. Various synthetic tests show that (1) reference station technique is not critically sensitive to varying crustal thicknesses between reference and target stations (2) the use of events with increased angle of incidence will cause deviations in split time delays (STD) with respect to the true value of the STD. Applying the reference station technique to the real data obtained from the INDEPTH IV and ASCENT seismic experiments at the northern margin of Tibet generally resulted in a good agreement between SKS- and direct S-derived splitting parameters. Where differences exist, the resolved shear waves fast polarization directions (FPD) indicate a higher degree of internal consistency for closely spaced stations where we do not expect clear lateral variation. This is probably due to the much larger number of S waves available for splitting measurements compared to SKS. Compared to SKS phases that are strongly restricted to the signal quality and a narrow range of angle of incidences, the use of direct S-waves increases the number of analyzed events by a factor of _4.

An important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting (SWS). In Sumatra, two temporary seismic networks were deployed between December 2007 and February 2009, covering the fore arc between the fore-arc islands to the back arc. We use SKS and local SWS measurements to determine the type, amount, and location of anisotropy. Local SWS measurements from the fore-arc islands exhibit trench-parallel fast directions which can be attributed to shape preferred orientation of cracks/fractures in the overriding sediments. In the Sumatran Fault region, the predominant fast direction is fault/ trench parallel, while in the back-arc region it is trench perpendicular. The trench-perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge, while the fault-parallel measurements are similar to the fault-parallel fast directions observed for two crustal events at the Sumatran Fault. This suggests that there are two layers of anisotropy: one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the Sumatran Fault. SKS splitting results show a NNW-SSE fast direction with delay times of 0.8–3.0 s. The fast directions are approximately parallel to the absolute plate motion of the subducting Indo-Australian Plate. The small delay times exhibited by the local SWS (0.05–0.45 s), in combination with the large SKS delay times, suggest that the anisotropy generating the teleseismic SWS is dominated by entrained flow in the asthenosphere below the slab.

Based on joint consideration of S receiver functions and surface-wave anisotropy we present evidence for the existence of a thick and layered lithosphere beneath the Kalahari Craton. Our results show that frozen-in anisotropy and compositional changes can generate sharp Mid-Lithospheric Discontinuities (MLD) at depths of 85 and 150–200 km, respectively. We found that a 50 km thick anisotropic layer, containing 3% S wave anisotropy and with a fast-velocity axis different from that in the layer beneath, can account for the first MLD at about 85 km depth. Significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere, as inferred from chemical tomography, and those of our second MLD led us to characterize it as a compositional boundary, most likely due to the modification of the cratonic mantle lithosphere by magma infiltration. The deepening of this boundary from 150 to 200 km is spatially correlated with the surficial expression of the Thabazimbi-Murchison Lineament (TML), implying that the TML isolates the lithosphere of the Limpopo terrane from that of the ancient Kaapvaal terrane. The largest velocity contrast (3.6–4.7%) is observed at a boundary located at depths of 260–280 km beneath the Archean domains and the older Proterozoic belt. This boundary most likely represents the lithosphereasthenosphere boundary, which shallows to about 200 km beneath the younger Proterozoic belt. Thus, the Kalahari lithosphere may have survived multiple episodes of intense magmatism and collisional rifting during the billions of years of its history, which left their imprint in its internal layering.

The territory of Lithuania and adjacent areas of the East European Craton have always been considered a region of low seismicity. Two recent earthquakes with magnitudes of more than 5 in the Kaliningrad District (Russian Federation) on 21 September 2004 motivated re-evaluation of the seismic hazard in Lithuania and adjacent territories. A new opportunity to study seismicity in the region is provided by the PASSEQ (Pasive Seismic Experiment) project that aimed to study the lithosphere–asthenosphere structure around the Trans-European Suture Zone. Twenty-six seismic stations of the PASSEQ temporary seismic array were installed in the territory of Lithuania. The stations recorded a number of local and regional seismic events originating from Lithuania and adjacent areas. This data can be used to answer the question of whether there exist seismically active tectonic zones in Lithuania that could be potentially hazardous for critical industrial facilities. Therefore, the aim of this paper is to find any natural tectonic seismic events in Lithuania and to obtain more general view of seismicity in the region. In order to do this, we make a manual review of the continuous data recorded by the PASSEQ seismic stations in Lithuania. From the good quality data, we select and relocate 45 local seismic events using the well-known LocSAT and VELEST location algortithms. In order to discriminate between possible natural events, underwater explosions and on-shore blasts, we analyse spatial distribution of epicenters and temporal distribution of origin times and perform both visual analysis of waveforms and spectral analysis of recordings. We show that the relocated seismic events can be grouped into five clusters (groups) according to their epicenter coordinates and origin and that several seismic events might be of tectonic origin. We also show that several events from the off-shore region in the Baltic Sea (at the coasts of the Kaliningrad District of the Russian Federation) are non-volcanic tremors, although the origin of these tremor-type events is not clear.

The Himalaya and the Tibetan Plateau are uplifted by the ongoing northward underthrusting of the Indian continental lithosphere below Tibet resulting in lithospheric stacking. The layered structure of the Tibetan upper mantle is imaged by seismic methods, most detailed with the receiver function method. Tibet is considered as a place where the development of a future craton is currently under way. Here we study the upper mantle from Germany to northern Sweden with seismic S receiver functions and compare the structure below Scandinavia with that below Tibet. Below Proterozoic Scandinavia, we found two low-velocity zones on top of each other, separated by a high-velocity zone. The top of the upper low-velocity zone at about 100 km depth extends from Germany to Archaean northern Sweden. It agrees with the lithosphere-asthenosphere boundary (LAB) below Germany and Denmark. Below Sweden it is known as the 8°discontinuity, or as a mid-lithospheric discontinuity (MLD), similar to observations in North America. Seismic tomography places the LAB near 200 km in Scandinavia, which is close to the top of our deeper low-velocity zone. We also observed the bottom of the asthenosphere (the Lehmann discontinuity) deepening from 180 km in Germany to 260 km below Sweden. Remnants of old subduction in the upper about 100 km below Scandinavia and Finland are known from controlled source seismic experiments and local earthquake studies. Recent tomographic studies indicate delamination of the lithosphere below southern Scandinavia and northern Germany. We are suggesting that the large-scale layered structure in the Scandinavian upper mantle may be caused by processes similar to the ongoing lithospheric stacking in Tibet.

We present a series of 1-D shear velocity models for the Sumatran Forearc and Arc derived from Rayleigh wave group dispersion in noise correlation functions from vertical and pressure records from an onshore–offshore seismic deployment. The 1-D models represent the crustal structure of the downgoing Indian Plate, the accretionary prism and the arc. There is a progression in shear velocity across the forearc to the arc associated with thickening of the accretionary prism and the development of an arc crust. The velocity structure inferred for the upper 20 km based on path averages between stations on the accretionary prism has velocities consistent with a thick sediment package in agreement with estimates of depth to the plate boundary determined from active source experiments. We also find low Indian Plate shear velocities

On 27 February 2010 the Mw 8.8 Maule earthquake in Central Chile ruptured a seismic gap where significant strain had accumulated since 1835. With a magnitude of 8.8, it is the sixth-strongest earthquake since the beginning of the instrumental record; rapid response teams from Chile, the US, Germany and the UK installed a dense network for monitoring aftershocks along the whole rupture zone. We analysed a subset of this network (in total 139 stations) and detected over 100000 aftershocks following the main earthquake in the period from March to September 2010 alone, using automatic detection algorithms. Picks are refined by an auto-picking algorithm (MPX) and events are relocated in a minimum-1D model. About 20000 events are designated as very well located with at least 16 high quality automatic picks and a residual rms no larger than 0.2 s. Besides crustal seismicity, the aftershock sequence is dominated by intense plate interface seismicity near and immediately downdip of the most intense coseismic rupture. We also observe a second separate band of deeper aftershocks below the downdip end of the seismogenic zone at a depth of 40-50 km and a distance to the trench of 130-180 km, with a gap of 20-30 km to the main plate interface seismicity. In this presentation we concentrate on the analysis of this deep seismic band. The seismicity in this band is not truly continuous along the rupture zone but it is present along the whole rupture zone and forms clusters elongated along strike. Focal mechanisms derived from first motion polarities show that these events tend to be thrust type events, well aligned with the plate interface. A second deep separate group of plate interface aftershocks is not known from other subduction zone aftershock sequences. To get a better idea about the distribution of these 6000 deep aftershocks (30 to 50 km), a waveform- and catalogue-based clustering of aftershocks was carried out, followed by double-difference relocation. We also identified over 700 groups of events with highly similar waveforms. Most of the clusters are doublets and triplets, but the largest cluster contains 12 events. In more than 50 clusters events occurred semi-periodically 6-8 times with intervals of around 2 weeks, suggesting these are repeating events. For about 3000 aftershocks in the deep band precise relative locations could be determined based on catalogue and waveform-based double difference times, with formal uncertainties down to 100 m.

As Alfred Wegener already recognized 100 years ago, the giant southern continent, Gondwanaland, broke about 200 million years ago into several pieces which drifted apart. One part, India, drifted northward until it collided 50 million years ago with Eurasia. This collision created the Himalayan mountain chain and the Tibetan plateau, which are not only very significant geological structures, but are also important parts of the Earth System. The influence of Tibet on the atmospheric circulation and world climate and the ongoing threat of giant collisional earthquakes to the megacities in the Ganges plain must be emphasized. In international cooperation, the GFZ conducted a number of seismic experiments in Tibet, known as INDEPTH experiments, to study details of the deformation of the tectonic plates as a consequence of the collision. As a result the presence of the Indian lithosphere was for the first time seismologically demonstrated to exist several hundred kilometers northwards below Tibet. During the collision the Indian crust was peeled off and contributes to the thickening of the Tibetan crust. The latest phase of the INDEPTH experiments was focused on the northern margin. Using active and passive seismic techniques (wide-angle profiling, receiver functions, surface wave tomography), we have imaged the deep structure below Tibet, showing the configuration of the Tibetan lithosphere between the Indian and Eurasian plates. We also found evidence for unusual properties of the lower crust, which are likely to be responsible for the prevalence of crustal flow in northern Tibet.

[1] The combination of the Sunda megathrust and the (strike-slip) Sumatran Fault (SF) represents a type example of slip-partitioning. However, superimposed on the SF are geometrical irregularities that disrupt the local strain field. The largest such feature is in central Sumatra where the SF splits into two fault strands up to 35 km apart. A dense local network was installed along a 350 km section around this bifurcation, registering 1016 crustal events between April 2008 and February 2009. 528 of these events, with magnitudes between 1.1 and 6.0, were located using the double-difference relative location method. These relative hypocentre locations reveal several new features about the crustal structure of the SF. Northwest and southeast of the bifurcation, where the SF has only one fault strand, seismicity is strongly focused below the surface trace, indicating a vertical fault that is seismogenic to ∼15 km depth. By contrast intense seismicity is observed within the bifurcation, displaying streaks in plan and cross-section that indicate a complex system of faults bisecting the bifurcation. In combination with analysis of topography and focal mechanisms, we propose that the bifurcation is a strike-slip duplex system with complex faulting between the two main fault branches.

The Sumatra subduction zone is located on the eastern side of the Sunda Arc between the Sunda Strait and the Andaman Islands, where the Indo-Australian plate is subducting beneath the Eurasian plate. An important tool in understanding the style and geometry of deformation within a subduction zone is the measurement of seismic anisotropy, through observations of shear wave splitting, which provides information about the mantle flow. In Sumatra two temporary seismic networks were deployed within the Mentawai and Northern region, between December 2007 and October 2008 and April 2008 and February 2009, respectively. Here we use new splitting measurements from SKS and local S phases from these networks, to characterize the type and amount of anisotropy within the region. High quality SKS splitting results obtained from 16 stations show a coherent fast direction of NNW (350°) to SSE (170°) with delay times of 1.0 to 3.0s. The observations do not conform to the standard classification of trench parallel and trench perpendicular, instead they are trench oblique, approximately parallel to the direction of motion of the subducting Indo-Australian plate. The magnitude and direction of splitting suggests that the anisotropy is due too entrained flow in the asthenosphere beneath the subducting lithosphere. Local S wave splitting measurements were obtained from 85 rays, generated by earthquakes at focal depths of 15 km-200 km and recorded across 39 stations. The polarization of the fast shear wave is trench parallel along the islands and can be contributed to shape preferred orientation of cracks in the top of the subducting slab and overriding crust. In the forearc a rotation in fast direction to trench perpendicular is observed, with a clear positive correlation between the distance the ray has traveled in the mantle and delay time, suggesting anisotropy originates from entrained flow within the mantle wedge. In the Sumatra fault region and the back arc, events originating at the plate interface show both trench perpendicular and trench parallel fast directions with delay times of up to 0.4 s, while shallow events on the Sumatra fault indicate a clear fault parallel direction with delay times of 0.1 s to 0.18 s. This pattern of shear wave splitting suggests layers of different anisotropy, one deeper layer due to entrained flow within the Sumatran mantle wedge causing trench perpendicular direction, and the second shallower one within the overriding crust due to shape preferred orientation possibly caused by the Sumatran Fault.

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 landstations was installed along the whole rupture zone in order to capture the aftershock activity. We present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines. Processing the seismic data between 15 March and 30 September 2010 from stations from IRIS, IPGP, Caltech and GFZ, we determined 19,908~hypocentres with magnitudes Mw between 1 and 6.2. 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. Along strike, the aftershocks occur largely within the zone of co-seismic slip but extend ~50 km further north. Along dip, the events are either within the zone of co-seismic slip, or downdip from it, depending on the 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 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the co-seismic rupture, and presumably above the intersection of the continental Moho with the plate interface. 4.) A deep group of intermediate depth events between 80 to 120 km depth are present north of 36°S. 5.) The magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mainshock 6.) Pronounced crustal aftershock activity is found in the region of Pichilemu (~34.5°S). The time-series of postseismic deformation analyzed here show rapid transient deformation immediately following the Maule earthquake. We examine the relation between the spatial-temporal properties of the aftershock distribution and postseismic displacements from GPS. First results show a linear relationship between cumulative displacement and cumulative number of aftershocks at large times (>25d, when the local aftershock catalog is available). This relationship may be use to infer rheological properties. Similar relations have been observed in other large subduction zone earthquakes.

Seismological imaging has identified the Indian lithosphere penetrating underneath Tibet up to 500km to the north and to a depth of at least 200km along a front that is more than 1000km long. This is a classical case of continental subduction. In contrast, the collision of Tibet with the stable Tarim Basin in the north-west caused thickening of the Tibetan lithosphere to about 200km, whereas collision with the Sichuan Basin in the east caused thinning of the Tibetan lithosphere to about 70km. No sufficient seismic data on the mantle lithosphere have been available up to now at the boundary of Tibet to the Qaidam Basin, where subduction of the Asian lithosphere beneath Tibet was suggested. We report on results from a recent seismic passive source experiment in this region, which continued the series of INDEPTH experiments to the Qaidam Basin in the north-east. We used the S receiver function technique for data analysis, which is especially sensitive for observations of the lithosphere-asthenosphere boundary (LAB). As a surprising result, we found evidence that a newly identified relatively thin Tibetan lithosphere is overriding the flat subducting Asian lithosphere.

Recent studies have suggested that uplift of the northern Tibetan plateau may be related to removal of lithospheric mantle, resulting in emplacement of hotter, less dense asthenosphere. Other studies propose that plateau uplift and crustal thickening have occurred through a process of lateral mid-crustal flow or coherent deformation between crust and lithospheric mantle. Some authors attribute the geophysical properties of upper mantle beneath the plateau to either delamination of thickened lithosphere, or asthenospheric counterflow associated with subduction of continental Indian lithosphere beneath central Tibet. In order to study the evolution and dynamics of the Tibetan plateau, we deployed 74 broadband seismic stations throughout northeastern Tibet within the scope of ASCENT/INDEPTH-IV experiment. In conjunction with Namche Barwa data, we have calculated fundamental mode Rayleigh wave phase velocities utilizing two-plane wave approach, for periods between 20-143 seconds. We also obtained preliminary phase velocities using Love waves. To invert for shear wave velocities, we use partial derivatives from Saito (1988), assuming a constant Poisson’s ratio. Our azimuthal anisotropy measurements agree well with SKS splitting results; both indicate significant (>2%) average azimuthal anisotropy throughout the upper mantle down to depths exceeding 250 km, with a dominantly EW fast directions. Although we observe variations of fast directions with depth, they are generally consistent (i.e., within 15 degrees) up to ~200 km, indicative of vertically coherent deformation. Furthermore at crustal depths, azimuthal fast directions tend be sub-parallel to the strikes of major strike slip faults, suggesting that shearing is the dominant deformation mechanism in eastern Tibet. Our tomographic models show an uppermost mantle low velocity anomaly north of Bangong-Nujiang Suture (BNS) in northeastern Tibet, and a high velocity anomaly extending ~200 km centered on the BNS. We suggest that the low velocity zone is due to warmer, thinner lithosphere in the northern Qiangtang and Songpan-Ganzi terranes. At depth, we observe high velocity bodies to the south both in our phase velocity and shear wave velocity maps, indicative of an underthrusting Indian lithosphere. Our phase maps and shear wave velocity-anomaly isosurfaces strongly indicate that underthrusting of Indian plate is sub-horizontal, has variable geometry in EW direction, and does not extend north of the BNS. We propose that underthrusting is accompanied by lateral tearing along old weak zones into at least two fragments, and subsequent break-off of the western-most portion. Our models reveal low velocity zones concentrated along major strike slip faults, which we attribute to strain heating. Furthermore, the Qiadam Basin is characterized by high velocities in the mantle, and moderate to slow velocities below the Kunlun Shan and northern Qiangtang argue against continental subduction.

On 27 February 2010 theMw 8.8 Maule earthquake in Central Chile ruptured a well known seismic gap, which last broke in 1835. Shortly after the mainshock, Chilean agencies (UC Santiago, UC Concepción) and the international seismological community (USA (IRIS), France (IPGP), UK (University of Liverpool), Germany (GFZ)) installed a total of 142 portable seismic stations along the whole rupture zone in order to capture the aftershock activity. Most stations were in the field until September 2010, with a subset remaining until January 2011; the UK stations will remain in the field beyond this time. The data from the initial deployment are open and are being distributed through the IRIS and GEOFON data centres. We will present preliminary aftershock distributions based on automatic detection algorithms. In total, for the period between March and September 2010 we detected _60,000 locatable earthquakes, of which we form a subset of _7,000 events with high quality locations. The depth of events in the high quality subset is generally well constrained such that the plate interface is clearly defined, and can be separated from overriding plate seismicity. First order features that can be identified are: 1.) A pronounced cluster of seismicity is apparent at 25-35 km depth and 50-120 km perpendicular distance from the trench (with some NS variation). 2.) A secondary band of seismicity can be identified at 40-50 km depth and _150-160 km perpendicular trench distance and between 34_ and 37_S. Although the secondary band lies along the continuation of the primary one, it is clearly separated from it by a gap with sparse seismicity. 3.) Intense crustal seismicity is found in the region of Pichilemu. This region hosted the strongest aftershock (Mw=6.9), a normal faulting event with NW strike. The aftershocks extend from the plate interface to the surface and are aligned on a NNW-SSE oriented band in map view. 4.) An isolated shallow cluster of crustal seismicity occurs beneath the volcanic arc (36.42_S, 71.1_W) near Laguna del Dial. Ongoing research is concerned with calculating first motion focal mechanisms for the larger events and improving locations by relative location methods.

Over the last 20 years project INDEPTH has helped to image the underthrusting Indian continental lithosphere, crustal low velocity zones, and large changes in seismic anisotropy that correspond with the major tectonic blocks that make up the plateau. INDEPTH-IV differed with the prior INDPEPTH phases by having a 2-D seismic array as well as with resolution profiles. This 2D array combined with other 2-D arrays across the eastern edge of the plateau have helped to give a new high resolution three dimensional picture of crustal and upper mantle structure in this important region. Current velocity models of the Tibetan Plateau have had uniform structure parallel to the Himalaya and major east-west suture zones; however, our new images have significant orogen-parallel variability in upper-mantle seismic velocities. In general the upper mantle, from the Main Frontal Thrust to central Tibet around 33°-34°N, exhibits laterally variable P- and S-wave velocity anomalies extending to at least 250 km in depth. Significant low velocity anomalies are observed beneath southern Tibet, elongated in a north-south direction and extending to at least 150 km depth, possibly deeper. These slow velocity anomalies can be interpreted as evidence for fragmentation of the UICL as it is forced beneath the overriding Tibetan lithosphere. In contrast, the upper mantle of the northern Qiangtang terrane and Songpan-Ganzi terrane shows a homogeneous low velocity zone with no sign of a southward subduction of the Asian continental lithosphere. We also find consistent results between the velocity and attenuation tomography. QLg and QPg models show a high seismic attenuation zone along the Kunlun belt. Similarly, a high velocity and high Q block are observed in southeastern Tibet around the eastern Bangong-Nujiang Suture and Eastern Himalaya Syntaxis. There is a significant azimuthal anisotropy of seismic Q. The isotropic seismic Q, suggested as an estimate of Q of the crust, is low in northern Qiangtang and the Songpan-Ganzi. The high-Q directions parallel major fault planes in eastern Tibet, and correlate with the fast-direction of shear wave splitting and Rayleigh wave azimuthal anisotropy, suggesting coherent deformation between the crust and upper mantle in this region

The temporary installation of seismic stations in West Sumatera and Mentawai islands in collaboration with UK universities, the British Geological Survey, the GFZ Potsdam, and Indonesian institutions led us to conduct a study on identifying the crustal structure beneath the area mentioned above. The stations consisted of 10 broadband (CMG-3T) and 70 short period (CMG-6T) seismometers and were installed during April 2008 and March 2009. In total, waveforms from 56 teleseismic events with Mw of 6 - 7.7 yielded usable data. The method used in this study is the teleseismic receiver functions. To estimate the receiver function, we use an iterative deconvolution approach. This approach minimizes the difference between observed seismogram and predicted signals with least-square principle. In order to determine crustal thickness and average crustal Vp/Vs, we employ the H_ stacking method by summing amplitudes at predicted arrival times of the Moho Ps conversion phase and its multiples for different crustal thickness (H) and Vp/Vs ratio (_). Migrated receiver functions images of the mainland of Sumatera show a clearer reflectivity than those below the island. A negative reflection is obtained below mainland station B50B, due to the location of this station is close to a volcano. An ambiguity exists on the island images, a semi-coherent phase at 50 km might be interpreted as Moho without any geological information. The other shows negative polarity with low consistency. This can be an effect of shallow structure or serpentinization. From the best stacked receiver function images, the average Moho depth is 30 km, varying from 22 to 40 km. Generally, the Moho is deepest under the volcanic arc.

We invert a data set of more than 26,000 teleseismic P-wave arrival times to determine the variation in compressional wave structure beneath NE Tibet. The seismograms from which the arrival times were read were recorded from 572 events at 80 stations from the ASCENT and INDEPTH IV experiments from 2007-2009. The motivation for the experiments was to extend earlier seismic surveys to the edge of the plateau, and consider an area which contains the Kunlun Fault, and the Jinsha and Bangong-Nujiang sutures. The experiments are intended to resolve issues such as how deep the fault zones extend, the variation in Moho depth across the region, and consider the viability of the crustal flow hypothesis. The resulting tomographic models show a number of large scale features. There is a slow anomaly extending to 400km depth across the Kunlun Qaidam and Songpan Ganzi terranes, from approximately 91 _E to 95 _E. There is an extensive fast region across the Qiantang from 31 _N to 34 _N and 90 _E to 94 _E, which also appears to persist to 400km depth. There is a deep, fast anomaly across the Qaidam Basin, with a sharp transition to slower material to the south. The resolution tests suggest that resolution of features tens of kilometres wide is possible, but with significant smearing (particularly in the vertical direction).

Ambient noise tomography is applied to the significant data resources now available across Tibet and surrounding regions to produce Rayleigh wave phase speed maps at periods between 6 and 50 s. Data resources include the permanent Federation of Digital Seismographic Networks, five temporary U.S. Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) experiments in and around Tibet, and Chinese provincial networks surrounding Tibet from 2003 to 2009, totaling ∼600 stations and ∼150,000 interstation paths. With such a heterogeneous data set, data quality control is of utmost importance. We apply conservative data quality control criteria to accept between ∼5000 and ∼45,000 measurements as a function of period, which produce a lateral resolution between 100 and 200 km across most of the Tibetan Plateau and adjacent regions to the east. Misfits to the accepted measurements among PASSCAL stations and among Chinese stations are similar, with a standard deviation of ∼1.7 s, which indicates that the final dispersion measurements from Chinese and PASSCAL stations are of similar quality. Phase velocities across the Tibetan Plateau are lower, on average, than those in the surrounding nonbasin regions. Phase velocities in northern Tibet are lower than those in southern Tibet, perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained. At short periods (20 s), very high velocities are imaged in the Tarim Basin, the Ordos Block, and the Sichuan Basin. These phase velocity dispersion maps provide information needed to construct a 3-D shear velocity model of the crust across the Tibetan Plateau and surrounding regions.