IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

1W_2F-P23

Date/Time: July 21 Poster

Enhanced sub-daily near real-time surface deformation analysis at Deception (SouthShetland) and El Hierro (Canaries) Islands
Goncalo Prates1 , Manuel Berrocoso1 , Alberto Fernandez-Ros1 , Jose Manuel Marrero2 , Ramon Ortiz2 ,Alicia Garcia2
1

Laboratorio de Astronomia, Geodesia y Cartografia - Universidad de Cadiz, Spain, 2 Instituto deGeociencias - Consejo Superior de Investigaciones Cientificas, Spain
E-mail: gprates@ualg.pt

A methodology for near real-time surface deformation analysis was developed and applied at Deception Island. It
relies on a minimum of three strategically deployed benchmarks’ position variations at sub-daily rates determinedby GNSS-GPS (Global Navigation Satellite Systems - Global Positioning System) geodetic techniques. The
benchmarks’ positions were reached every 30 minutes with the double-differenced ionosphere-free combination,a 10 degrees cut-off angle and precise ultra-rapid ephemerides, along with pre-processed 3-hourly ambiguity
solutions and hourly tropospheric zenith delay corrections. Multipath and residual loading and meteorologicaleffects were further dealt by a discrete Kalman filter. The method’s position accuracy was accessed at 1mm
in the northing and easting components and 2mm in the height component, when applied to baselines up
to 300km, with a reference benchmark that is far away from the volcano’s dynamic influence. Supported on
accurate benchmarks’ positions, a normal vector analysis was applied to triangles covering the monitored surface
determining instantaneous strain and inclination.
In Deception Island significant ground deformation was identified in the 2003-2004 campaign before a three
years extension process with an acceleration present throughout the 2006-2007 campaign. Along the 2003-2004
campaign the highest number of LP events was detected since the Spanish Antarctic campaigns are carried out,
and an increase in the sulphur dioxide flow was detected. As the geodetic campaign ended in 2003-December while
the LP events increase begun in 2004-January, ground deformation was precursory to the LP events and sulphur
dioxide flow increases. Conversely, the three years extension process had no reported significant seismic activity
or increase of gas emissions, with the 2006-2007 austral summer having one of the lowest number of detected
seismic events per day. This seismic calmness contrasts with the campaign’s 23 ppm/year triangle’s extension rate.
These methods were also applied in El Hierro Island during its unrest and eruption. Along the process all available
benchmarks’ position time series were made accessible in near real-time. Nine days before the eruption isdetected through a volcanic tremor, a sudden southwards deformation for two days followed by a strong northwards
compensation is identified. Some larger magnitude seismic events accompany these strong trend shifts. Thissequence may be related to a rupture along the magma pathway, with fluid pressure decrease and its stabilization
after. A correlation was also identified between ground deformation and larger magnitude seismicity. Several times
an increase in height precedes a sequence of seismic events while heights decrease. The same can be observed in
the northing component where these seismic events accompany southwards deformation. The ground deformation
was precursor to the seismic activity, but also was influenced by seismic activity.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

522