S U M M A R YWith its remote location in the ice-covered Fram Strait, Lena Trough is a poorly known segment of the global mid-ocean ridge system. It is a prominent member of the ultra-slow spreading mid-ocean ridges but its spreading mechanisms are not well understood. We relocalized teleseismically recorded earthquakes from the past five decades to identify tectonic processes in Lena Trough and the adjacent Spitsbergen Fracture Zone (FZ). During two cruises with RV Polarstern in 2008 and 2009 we deployed seismic arrays on ice floes to record the local seismicity of Lena Trough. We could identify and localize microseismic events which we assume to be present in the entire rift valley. In contrast, our relocalization of teleseismically recorded earthquakes shows an asymmetric epicentre distribution along Lena Trough with earthquakes occurring predominately along the western valley flanks of Lena Trough. In 2009 February/March, several high-magnitude earthquakes peaking in an M b 6.6 event occurred in an outside-corner setting of the Spitsbergen FZ. This is the strongest earthquake which has ever been recorded in Fram Strait and its location at the outside-corner high of the ultra-slow spreading ridge is exceptional. Comparing the seismicity with the magnetic anomalies and high-resolution multibeam bathymetry, we divide Lena Trough in a symmetrically spreading northern part and an asymmetrically spreading southern part south of the South Lena FZ. We propose that a complex interaction between the former De Geer Megashear zone, which separated Greenland from Svalbard starting at Late Mesozoic/Early Cenozoic times, and the developing rift in the southern Lena Trough resulted an increasing eastward dislocation towards the Spitsbergen FZ between older spreading axes and the recent active spreading axis which we believe to be located west of the bathymetric rift valley flanks in a wide extensional plain.

Geomorphic and morphometric data imply that process rates of the Schimbrig landslide, located in the Entle watershed (Central Switzerland), are still limited by the elevation of the LGM base level. At present, the Entle watershed is in a stage of adjusting to the lowered post-glacial base level as indicated by knick zones in the trunk stream. Some thousands of years later when these knick zones will reach the Schimbrig site, we anticipate a substantial increase in process rates and sediment flux for the landslide.The pattern of slip rates was measured on the Schimbrig landslide over a 14-months period. We propose that a Bingham plastic model explains much of how measured slip rates are linked to the observed topography, climatic variations and thickness variability of the landslide mass. This model explains why slip rates have been highest where the thickness of the material is substantially higher. It also explains why slip rates are highest in late summer/autumn and early spring. It appears then that snow melt in spring and decreasing temperatures in late summer/autumn potentially result in a high retention of the pore water and thus in a low viscosity of the material, which, in turns, promotes slip rates. Interestingly, an extreme rainstorm like the one of August 2005 only had a local impact on the landslide mass by triggering small scale earth flows and debris flows. This implies that the earth slide material does not directly respond to an episodic pattern of rainfall. Such precipitation events, however, superimpose a smaller-scale imprint on the landslide relief.

SUMMARY The ultraslow spreading Southwest Indian Ridge (SWIR) is a prominent end‐member of the global mid‐ocean ridge system. It spreads with a full‐rate of 14–16 mm y−1 and shows several segments of various obliquities. The western SWIR consists of the Oblique and Orthogonal Supersegments lying at an epicentral distance of ∼21° to the VNA2 seismic array operated by the German Neumayer station in East Antarctica. The array monitors backazimuth, apparent velocity and signal‐to‐noise ratio of arriving waves and provides a data set of seismicity from the western SWIR over several years. Compared to the global seismological network, its detection threshold for earthquakes occurring at the western SWIR is more than 0.5 mb lower enabling a more comprehensive study of mid‐ocean ridge processes than the teleseismic earthquake catalogues. We identified a total number of 743 earthquakes occurring at the western part of the SWIR and calculated the body‐wave magnitudes (mb) from P‐wave amplitude picks on the VNA2 broad‐band sensor obtaining a magnitude range from mb 3.18 to mb 5.34. In the years of 2001, 2004, 2005 and 2008, significantly increased event rates indicated four earthquake swarms with up to 164 events lasting for several days. All swarms had strong events registered in the International Seismological Centre catalogue. The relocalization of these events confirmed that all swarms occurred in the same region on the Orthogonal Supersegment. We analysed event and moment release rate histories, b‐values and aftershock decay rates (Modified Omori Law) finding that the swarms of 2001, 2004 and 2005 have similarities in the temporal distribution of seismic moment and event numbers. The swarm of 2008 is smaller with high magnitude events at the swarm's onset which represent shear failure on normal faults. The application of the Modified Omori Law and the b‐value show that the earthquakes of the swarms do not follow the classical main shock–aftershock pattern of purely tectonic earthquake sequences. At the Orthogonal Supersegment, a continuous positive magnetic anomaly along the rift axis, a negative mantle Bouguer anomaly, basalts at the seafloor and potentially volcanic edifices indicate robust magmatic crustal accretion. The high‐resolution bathymetry shows ubiquitous rift‐parallel ridges with steep flanks towards the rift axis indicating high‐angle normal faults. The high‐magnitude earthquakes detected teleseismically during the swarms are generated there. We interpret that the swarms are caused by magmatic accretion episodes at a suggested volcanic centre of the Orthogonal Supersegment and that possible magma injection activates the steeply dipping fault planes.

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