HR: 10:35h
AN: G52A-02 INVITED     [Abstracts]
TI: Rapid Inflation Followed by Trapdoor Faulting in April 2005, Measured by Continuous GPS and InSAR at Sierra Negra Volcano, Galapagos
AU: * Geist, D
EM: dgeist@uidaho.edu
AF: University of Idaho, Geology, Moscow, ID 83844
AU: Johnson, D
EM: dj@ess.washington.edu
AF: UPS, Geology, Tacoma, WA 98416 United States
AU: Chadwick, W
EM: bill.chadwick@noaa.gov
AF: OSU/Noaa, Hatfield Center, Newport, OR 97365
AU: Jonsson, S
EM: jonsson@tomo.ig.erdw.ethz.ch
AF: ETH, Geophysics, Zurich, 8092 Swaziland
AU: Poland, M
EM: mpoland@usgs.gov
AF: USGS, HVO, Volcano, HI 96718
AU: Meertens, C
EM: chuckm@unavco.org
AF: Unavco, 6350 Nautilus, Boulder, CO 80301
AU: Gallagher, W
EM: gallaher@unavco.org
AF: Unavco, 6350 Nautilus, Boulder, CO 80301
AU: Feaux, K
EM: feaux@unavco.org
AF: Unavco, 6350 Nautilus, Boulder, CO 80301
AB: On April 16, 2005, a trapdoor fault in the floor of Sierra Negra's caldera slipped approximately 85 cm in less than 10 seconds, during a M4.6 earthquake. This trapdoor-faulting event followed about 2 years of accelerating inflation (up to a rate of 2 m/y) and is similar to a previous faulting event documented by satellite radar interferometry (InSAR) in 1997-8. The 2005 event was captured in unprecedented detail by a new continuous global positioning system (CGPS) network installed in 2002. Modeling of the CGPS data along with results from satellite radar interferometry give a more refined interpretation of the nature of trapdoor faulting events. In particular this event (and by inference the 1997-8 faulting event) are modeled as a thrust rather than a normal fault. The new models indicate that trapdoor faulting at Sierra Negra is a direct consequence of rapid magmatic intrusion, and the two processes appear to be in a long-term feedback relationship in which faulting relieves strain accumulated by inflation and probably postpones eruptions. The caldera-wide uplift that preceded the faulting was almost certainly caused by the intrusion of > 10⁷ m³ of magma beneath the caldera. Moreover, we hypothesize that the pressurization of the shallow magma body, which modeling indicates is a 2-km deep, flat-topped magma chamber, results in redissolution of newly-formed vesicles. In contrast, sudden elastic failure of the roof results in a sudden depressurization and vesiculation of the magma. Microgravity measurements spanning the inflation and trapdoor faulting events indicate that the pressure increase and consequent magma compression during the elastic inflation was released during the trapdoor uplift. These observations suggest that the caldera floor is unusually weak. Since the rate of inflation was not slowed by the 2005 faulting event, we expect either more faulting events or an eruption in the near future.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8419 Volcano monitoring (7280)
DE: 8434 Magma migration and fragmentation
DE: 8439 Physics and chemistry of magma bodies
SC: Geodesy [G]
MN: Fall Meeting 2005