Earthquake risk on the Sunda trench

On 28 March 2005 the Sunda megathrust in Indonesia ruptured again, producing another great earthquake three months after the previous one. The rupture was contiguous with that of the December 2004 Sumatra–Andaman earthquake, and is likely to have been sparked by local stress, although the triggering stresses at its hypocentre were very small — of the order of just 0.1 bar. Calculations show that stresses imposed by the second rupture have brought closer to failure the megathrust immediately to the south, under the Batu and Mentawai islands, and have expanded the area of increased stress on the Sumatra fault. Palaeoseismologic studies show that the Mentawai segment of the Sunda megathrust is well advanced in its seismic cycle and is therefore a good candidate for triggered failure

Indonesian earthquake: Earthquake risk from co-seismic stress.

Following the massive loss of life caused by the Sumatra-Andaman earthquake in Indonesia and its tsunami, the possibility of a triggered earthquake on the contiguous Sunda trench subduction zone is a real concern. We have calculated the distributions of co-seismic stress on this zone, as well as on the neighbouring, vertical strike-slip Sumatra fault, and find an increase in stress on both structures that significantly boosts the already considerable earthquake hazard posed by them. In particular, the increased potential for a large subduction-zone event in this region, with the concomitant risk of another tsunami, makes the need for a tsunami warning system in the Indian Ocean all the more urgent.John McCloskey, Suleyman S.Nalbant, Sandy Steac

Social Participation and Disaster Risk Reduction Behaviors in Tsunami Prone Areas

This paper examines the relationships between social participation and disaster risk reduction actions. A survey of 557 households in tsunami prone areas in Phang Nga, Thailand was conducted following the 2012 Indian Ocean earthquakes. We use a multivariate probit model to jointly estimate the likelihood of undertaking three responses to earthquake and tsunami hazards (namely, (1) following disaster-related news closely, (2) preparing emergency kits and/or having a family emergency plan, and (3) having an intention to migrate) and community participation.We find that those who experienced losses from the 2004 tsunami are more likely to participate in community activities and respond to earthquake hazards. Compared to men, women are more likely to prepare emergency kits and/or have an emergency plan and have a greater intention to migrate. Living in a community with a higher proportion of women with tertiary education increases the probability of engaging in community activities and carrying out disaster risk reduction measures. Individuals who participate in village-based activities are 5.2% more likely to undertake all three risk reduction actions compared to those not engaging in community activities. This implies that encouraging participation in community activities can have positive externalities in disaster mitigation

Erratum to: Seismic waves in 3-D: from mantle asymmetries to reliable seismic hazard assessment

Acknowledgments This paper is strongly relying upon the work of many colleagues and collaborators to whom we are greatly thankful, in particular: Carlo Doglioni, Gillian Foulger, Vahid Gholami, Hossein Hamzehloo, Volodya Kossobokov, Cristina La Mura, Anatoly Levshin, Andrea Magrin, Antonella Peresan, Federica Riguzzi, Franco Vaccari, Peter Varga, Tatiana Yanovskaya. Financial support from PRIN 2010-2011 and RITMARE projects, funded by Italian Ministry of University and Research, is gratefully acknowledged. In addition, Fig. 3 should be updated by new one as below

Clues from joint inversion of tsunami and geodetic data of the 2011 Tohoku-oki earthquake

The 2011 Tohoku-oki (Mw 9.1) earthquake is so far the best-observed megathrust rupture, which allowed the collection of unprecedented offshore data. The joint inversion of tsunami waveforms (DART buoys, bottom pressure sensors, coastal wave gauges, and GPS-buoys) and static geodetic data (onshore GPS, seafloor displacements obtained by a GPS/acoustic combination technique), allows us to retrieve the slip distribution on a non-planar fault. We show that the inclusion of near-source data is necessary to image the details of slip pattern (maximum slip ~48 m, up to ~35 m close to the Japan trench), which generated the large and shallow seafloor coseismic deformations and the devastating inundation of the Japanese coast. We investigate the relation between the spatial distribution of previously inferred interseismic coupling and coseismic slip and we highlight the importance of seafloor geodetic measurements to constrain the interseismic coupling, which is one of the key-elements for long-term earthquake and tsunami hazard assessment

Rare dynamic triggering of remote M ≥ 5.5 earthquakes from global catalog analysis

Probing the effects of a transient stress on the timing of an earthquake occurrence is necessary for understanding the remote interaction of large-magnitude events. Global catalog data containing 35 years of M ≥ 5.5 earthquakes allow us to explore for periods of enhanced or suppressed seismic activity. We consider 113 M ≥ 7.5 main shocks between 1977 and 2012 and focus on seismic activity on time scales from seconds to days following these main shocks. We search for evidence of dynamic triggering of large-magnitude events similar to the previously observed global increase during the first few days following the 2012 M8.6 Indian Ocean main shock. We restrict the analysis to regions of elevated strain during the passage of surface waves. Using a threshold of 0.1 microstrain (∼3 kPa) and a temporal window of ±1 year, we stack daily seismicity rate curves using the exclusion-zone declustered M ≥ 5.5 catalog events in order to resolve deviations from the background rate. Our results do not indicate a significant change in activity for at least 10 days when considering the collective set of 113 main shocks and subsets at M8.0 and M8.5 thresholds. The results also do not indicate immediate triggering of M ≥ 5.5 events. We do find two instances of increased seismicity in the elevated strain region within 10 days. These increases are subsequent to two main shocks, the 1977 M8.3 and 2012 M8.6, both located in the Indian Ocean. We conclude that a global change in M ≥ 5.5 earthquake rates following a transient stress from distant earthquakes is a rare occurrence