The puzzle of the 1996 Bárdarbunga, Iceland, earthquake: no volumetric component in the source mechanism
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Abstract
A volcanic earthquake with Mw 5.6 occurred beneath the Bárdarbunga caldera in Iceland on 29 September 1996. This earthquake is one of a decade-long sequence of 
events at Bárdarbunga 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% double-couple 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.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | The puzzle of the 1996 Bárdarbunga, 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 |
| Publication Date | September 23, 2009 |
| Year Published | 2009 |
| Language | English |
| Publisher | Seismological Society of America |
| Contributing office(s) | Earthquake Science Center |
| Description | 9 p. |
| First page | 3077 |
| Last page | 3085 |
| Country | Iceland |
| Other Geospatial | Bardarbunga |
| Online Only (Y/N) | N |
| Additional Online Files (Y/N) | N |