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

Tkalcic, H.; Dreger, D. S.; Foulger, G. R.; Julian, B. R.

Abstract:

A volcanic earthquake with M_w 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.

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Article

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70037370

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Tkalcic, H.; Dreger, D. S.; Foulger, G. R.; Julian, B. R.

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3085

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English

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Bulletin of the Seismological Society of America

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The puzzle of the 1996 B??rdarbunga, Iceland, earthquake: No volumetric component in the source mechanism; 2009; Article; Journal; Bulletin of the Seismological Society of America; Tkalcic, H.; Dreger, D. S.; Foulger, G. R.; Julian, B. R.