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| Titel |
Dyke Intrusion and Arrest in Harrat Lunayyir, western Saudi Arabia, in April-July 2009 |
| VerfasserIn |
Sigurjón Jónsson, John Pallister, Wendy McCausland, Salah El-Hadidy |
| 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 |
250038367
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| Zusammenfassung |
| Dyke intrusion in Harrat Lunayyir (also known as Harrat Al-Shaqah), one of the volcanic
provinces in Saudi Arabia, caused numerous small to moderate-sized earthquakes and
extensive surface faulting in April-July 2009. The most intensive earthquake activity took
place on 17-20 May when six magnitude 4.6-5.7 earthquakes occurred, resulting in some
structural damage and prompting the Saudi civil protection authorities to evacuate more than
30000 people from the area. While the earthquake activity significantly decreased after
20Â May, it continued throughout June and July with a few earthquakes as large as magnitude
~4, before quieting down in August.
Much of what we have learned about the activity comes from interferometric satellite
radar (InSAR) observations and from analysis of the seismic data collected by a broadband
seismic network that was installed soon after the earthquake swarm started in April. The
InSAR data show that large-scale (40 km à 40 km) east-west extension of over 1 m took
place as well as broad uplift amounting to over 40Â cm. The center of the uplifted area was
transected by northwest-trending graben subsidence of over 50Â cm, bounded by a single fault
to the southwest showing up to ~1Â m of faulting and by multiple smaller faults and cracks to
the northeast.
The observed deformation is well explained with a near-vertical dyke intrusion and
graben-bounding normal faulting. The strike of the model dyke is NNW-SSE, parallel to the
Red Sea rift, and its volume is about 0.13 km3. The modeling suggests that the shallowest
part of the dyke 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.
The main graben-bounding surface fault, to the southwest of the dyke, grew from ~3Â km
to ~8 km with the magnitude 5.7 earthquake on 19 May. Soon after this event the overall
earthquake activity dramatically declined. The faulting appears to have significantly changed
the stress state in the shallow part of the crust, leading to an arrest of the dyke and thus
preventing further vertical magma migration towards the surface. Crustal deformation
continued after the main shock, with 25% of the total deformation taking place after 27Â May,
which shows that significant amount of magma was added to the dyke without further vertical
magma migration. |
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