Douglas S. Dreger
Gillian R. Foulger
Bruce R. Julian
Hrvoje Tkalcic
2009
<p><span>A volcanic earthquake with </span><i>M</i><sub>w</sub><span> 5.6 occurred beneath the Bárdarbunga caldera in Iceland on 29 September 1996. This earthquake is one of a decade-long sequence of </span><span id="inline-formula-1" class="inline-formula"><img class="inline-graphic" src="http://bssa.geoscienceworld.org/content/99/5/3077/embed/inline-graphic-1.gif" alt="Graphic" /></span><span> 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.</span></p>
application/pdf
10.1785/0120080361
en
Seismological Society of America
The puzzle of the 1996 Bárdarbunga, Iceland, earthquake: no volumetric component in the source mechanism
article