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.
Suggested Citation
Tkalcic, H., Dreger, D.S., Foulger, G.R., Julian, B.R., 2009, The puzzle of the 1996 Bárdarbunga, Iceland, earthquake: no volumetric component in the source mechanism: Bulletin of the Seismological Society of America, v. 99, no. 5, p. 3077-3085, https://doi.org/10.1785/0120080361.
ISSN: 1943-3573 (online)
ISSN: 0037-1106 (print)
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 |