Tectonics or magma intrusion? -- new results from multi-parameter study at Gede Volcano, West Java, Indonesia

D Hidayat1, H Gunawan2, M Hendrasto2, A Basuki2, F Schwandner1, S Marcial1, S Kunrat2

1 Earth Observatory of Singapore, Nanyang Technological University2Center for Volcanology and Geological Hazard Mitigation, Indonesia

JAKARTAJAKARTA

DanauDanauJatiluhurJatiluhur

Pangrango

©2009 Google – Map Data ©2009 and Europa Technologies©2009 Google – Map Data ©2009 and Europa Technologies

BOGORBOGOR

Gede Volcano, West Java, Indonesia

Seismic behavior at Gede

Eruptive history of Gede

Monitoring SchemeFor Gede & Salak Volcanoes

Initial no of station: 2 (1-component)Currently: 9 stations (3 components: BB and short period)Planned: 1 CO2 flux monitoring

PUN

Drumplot during normal periodExample of data

Drumplot during swarm

Locatable VT at and around Gede Volcano May 2011– Aug 2012

no report

Gede Hypocenters May 2011 – 26 Feb 2012

Gede Hypocenters during swarm 27 Feb- 9 Apr 2012

Gede Hypocenters Aug 2012

Receiver function study reveals 2 low velocity zones under Gede

Gede Hypocenters during swarm vs Results from Receiver Function Study

Comparison with previous swarm

Hypocenters of 2012 swarmHypocenters of 1997 swarm

Tilt time-series

Tilt vector

Deformation monitoring by tiltmeters Jun-Jul 2011

Tilt time-series

Tilt vector 11/2011 – 26/02/2012

Deformation monitoring by tiltmeters (Nov 2011-Feb 2012)

Tilt time-series

Tilt vector

Deformation monitoring by tiltmeters (27 Feb ’12-Jun ‘12)

Tilt time-series

Tilt vector

Deformation monitoring by tiltmeters (Aug-Sep 2012)

2011-2012 flank CO2 flux :•Campaigns:

• May, Sept 2011 (n 134)• March 2012 (n 40)

•Method: • high resolution CO2

accumulation chamber(LICOR Li8100A)

• ~10 points/day, >3/site•Results [CO2 g/m2/d]:

• 019.8 mean (2011)112.5 max (2011)

• 011.7 mean (2012)043.4 max (2012)

Compare flanks Gede -Merapi mean ~40, max ~120 g/m2/day(9/2002 at Woro) Toutain et al. 2002, Figs.1,8

Flank CO2 flux measurement campaignsHighlight: 2011 NE sector: higher CO2 activity

Possible source causing the earthquakes:

-tectonic related earthquakes (faulting)

-DVT (distal VT)

Concluding Remarks-Prior to the swarm in Feb-Mar 2012 and Aug 2012, sequences of small earthquakes occurred along NE-SW across Gede and Pangrango.

-A short VT swarms occurred 27 Feb-8 Mar 2012. We postulates that there may be a magma intrusion under Gede volcano but do not lead to any eruption. Similar swarms occurred in 1997 were located under Gede Volcano.

-Tilt data suggest deformation is controlled by local tectonic until early Nov 2011. Then tilt vector change suggests inflation due to (possibly) magma intrusion, followed by swarm of earthquakes at the end of Feb 2012. Several months later tilt data is back to NE direction. While CO2 flux measurements around Gede suggest some high flux around NE from the volcano.

-Gede & Salak activity need to be continously monitored with multi-parameter stations as any larger swarm, deformation, or gas flux changes may lead to surface activity (eruption) which will affect people living around the volcano.

Thank you