Plate-boundary deformation associated with the great Sumatra–Andaman earthquake

The Sumatra–Andaman earthquake of 26 December 2004 is the first giant earthquake (moment magnitude M_w > 9.0) to have occurred since the advent of modern space-based geodesy and broadband seismology. It therefore provides an unprecedented opportunity to investigate the characteristics of one of these enormous and rare events. Here we report estimates of the ground displacement associated with this event, using near-field Global Positioning System (GPS) surveys in northwestern Sumatra combined with in situ and remote observations of the vertical motion of coral reefs. These data show that the earthquake was generated by rupture of the Sunda subduction megathrust over a distance of >1,500 kilometres and a width of <150 kilometres. Megathrust slip exceeded 20 metres offshore northern Sumatra, mostly at depths shallower than 30 kilometres. Comparison of the geodetically and seismically inferred slip distribution indicates that ~30 per cent additional fault slip accrued in the 1.5 months following the 500-second-long seismic rupture. Both seismic and aseismic slip before our re-occupation of GPS sites occurred on the shallow portion of the megathrust, where the large Aceh tsunami originated. Slip tapers off abruptly along strike beneath Simeulue Island at the southeastern edge of the rupture, where the earthquake nucleated and where an M_w = 7.2 earthquake occurred in late 2002. This edge also abuts the northern limit of slip in the 28 March 2005 M_w = 8.7 Nias–Simeulue earthquake

Atmospheric controls on ground and space-based remote detection of volcanic ash Injection into the atmosphere, and link to early warning systems for aviation hazard mitigation

Violent volcanic eruptions, common especially in Southeast Asia, posean ongoing serious threat to aviation and local communities. However, the physicalconditions at the eruptive vent are difficult to estimate. In order to tackle thisproblem, satellite imagery and infrasound can rapidly provide information aboutstrong eruptions of volcanoes not closely monitored by on-site instruments. Forexample, the recent infrasonic array at Singapore, installed to support the coverageof the International Monitoring System, allows identification of nearby eruptingvolcanoes based on the characteristics of the recorded signal. But, due to its locationclose to the equator, seasonal changes in the wind velocity structure of the atmospherestrongly affect its potential to detect small volcanic eruptions at certainazimuths. To overcome this limit, infrasound could be augmented with satellite data. Yet, with the high average cloud cover in Southeast Asia, there are alsochallenges to identify weak volcanic plumes using satellite based monitoringtechniques. In this chapter, we aim to examine the relative strengths and weaknessesof the two technologies to better understand the possibility to improveoverall detection capability by combining infrasound with satellite imagery