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The puzzle of the 1996 B??rdarbunga, Iceland, earthquake: No volumetric component in the source mechanism

Bulletin of the Seismological Society of America

By:
, , ,
DOI: 10.1785/0120080361

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Abstract

A volcanic earthquake with Mw 5:6 occurred beneath the B??rdarbunga caldera in Iceland on 29 September 1996. This earthquake is one of a decade-long sequence of M 5 events at B??rdarbunga with non-double-couple mechanisms in the Global Centroid Moment Tensor catalog. Fortunately, it was recorded well by the regional-scale Iceland Hotspot Project seismic experiment. We investigated the event with a complete moment tensor inversion method using regional long-period seismic waveforms and a composite structural model. The moment tensor inversion using data from stations of the Iceland Hotspot Project yields a non-double-couple solution with a 67% vertically oriented compensated linear vector dipole component, a 32% doublecouple component, and a statistically insignificant (2%) volumetric (isotropic) contraction. This indicates the absence of a net volumetric component, which is puzzling in the case of a large volcanic earthquake that apparently is not explained by shear slip on a planar fault. A possible volcanic mechanism that can produce an earthquake without a volumetric component involves two offset sources with similar but opposite volume changes. We show that although such a model cannot be ruled out, the circumstances under which it could happen are rare.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
The puzzle of the 1996 B??rdarbunga, Iceland, earthquake: No volumetric component in the source mechanism
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1785/0120080361
Volume
99
Issue:
5
Year Published:
2009
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Bulletin of the Seismological Society of America
First page:
3077
Last page:
3085
Number of Pages:
9