Magma Ascent to Submarine Volcanoes: Real-Time Monitoring by Means of Teleseismic Observations of Earthquake Swarms
Abstract
Earthquake swarm occurrence belongs to reliable indicators of magmatic activity in the Earth crust. Their occurrence beneath submarine portions of volcanic arcs brings valuable information on plumbing systems of this unsufficiently understood environment and reveals recently active submarine volcanoes. Utilisation of teleseismically recorded data (NEIC, GCMT Project) enables to observe magmatic activity in almost real time. We analysed seismicity pattern in two areas - the Andaman-Nicobar region in April 2012 and the southern Ryukyu in April 2013. In both regions, the swarms are situated 80-100 km above the Wadati-Benioff zone of the subducting slab. Foci of the swarm earthquakes delimit a seismogenic layer at depths between 9 - 35 km that should be formed by brittle and fractured rock environment. Repeated occurrence of earthquakes clustered in swarms excludes large accumulations of melted rocks in this layer. Magma reservoirs should be situated at depths greater than 35 km. Upward magma migration from deeper magma reservoirs to shallow magma chambers or to the seafloor induce earthquake swarms by increasing tectonic stress and/or decreasing friction at faults. Frequency of earthquake swarm occurrence in the investigated areas has made a volcanic eruption at the seafloor probable. Moreover, epicentral zones of the swarms often coincide with distinct elevations at the seafloor - seamounts and seamount ranges. High accuracy of global seismological data enabled also to observe migration of earthquakes during individual swarms (Fig. 1), probably reflecting dike and/or sill propagation. Triggering of earthquake swarms by distant strong earthquakes was repeatedly observed in the Andaman-Nicobar region. The presented study documents high accuracy of hypocentral determinations published by the above mentioned data centers and usefulness of the EHB relocation procedure. Epicentral map of the October 2002 earthquake swarm in southern Ryukyu showing E-W migration of events during the swarm. The swarm occurred during 29 hours on October 23 - 25 in the magnitude range 4.0 - 5.2. Open circles - epicenters of all 54 events of the swarm; red circles - epicenters of events that occurred in a particular time interval of the swarm development: (a) - starting 3 hours; (b) - following 4 hours; (c) - final 22 hours.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.V13H..07S
- Keywords:
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- 8434 VOLCANOLOGY Magma migration and fragmentation