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| Titel |
InSAR Observations of the 2009 Harrat Lunayyir (western Saudi Arabia) Dyke Intrusion and Post-Diking Deformation |
| VerfasserIn |
Sigurjón Jónsson, Zhong Lu, Paul Lundgren |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038376
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| Zusammenfassung |
| Interferometric Satellite Radar (InSAR) observations of one of the volcanic provinces in
western Saudi Arabia, Harrat Lunayyir (also known as Harrat Al-Shaqah), provide rich
information about the geometry and evolution of a dyke intrusion and surface faulting that
occurred in the region in April-July 2009. The first sign of activity was the start of a seismic
swarm on 24Â April that steadily intensified until six magnitude 4.6-5.7 earthquakes struck on
17-20Â May. More than 30000 people were evacuated from the area following the activity in
mid-May and stayed in the neighboring cities of Yanbu and Medina for several
weeks.
During the intensive activity in mid-May we sent a request for emergency satellite radar
data acquisitions to the European Space Agency and later activated an International Charter
to guarantee satellite data collection of the area. We have analyzed a number of Envisat,
ALOS, and TerraSAR-X interferograms of the area and the results are outstanding, owing
to the stable and vegetation-free surface conditions. Interferograms spanning the
main seismic activity in mid-May exhibit strong deformation that extends across a
large 40Â km ÃÂ 40Â km area, with broad uplift and over a meter of WSW-ENE
extension. In addition, the data show clear signs of surface faulting and graben-like
subsidence in the middle of the deformed area with the graben subsidence exceeding
50Â cm.
Modeling of deformation strongly suggests that a near-vertical dyke intruded with a
WNW-ESE orientation, parallel to the Red Sea, and that the intruded volume is ~0.13
km3. The dyke intrusion appears to have triggered faulting on graben-bounding and
inward-dipping normal faults. The shallowest part of the dyke seems to have reached within
only 2Â km of the surface, right below where the graben is the narrowest and under an area
with a number of cinder cones from previous volcanic events.
While the day-to-day temporal evolution of the deformation cannot be derived from the
InSAR data, the limited SAR acquisitions reveal an interesting story. No significant
deformation is found before 8Â May despite strong increase in seismic activity from the start
of the earthquake swarm in April and until that time. The next SAR acquisition was
on 27Â May and the InSAR data show that 75% of the overall deformation was
completed by that time, with further 20% occurring between 27Â May and 17Â June,
and the remaining 5% in late June and July. This shows that significant part of the
intruded magma was added to the dyke after the period of intensive seismicity in mid
May.
The pattern of deformation in May, June, and July is very similar; only the amplitude is
different. This indicates that the geometry of the intruding dyke did not change significantly
when more magma was added to the system in June and July. It also shows that the numerous
surface faults continued to move with increasing dyke volume, but that no new surface faults
were activated after 27Â May. |
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