Time‐Dependent Spatial Amplitude Patterns of Harmonic Tremor at Arenal Volcano, Costa Rica: Seismic‐Wave Interferences?

Abstract : Seismograms recorded at the receivers of a small-aperture seismic array usually display very similar waveforms and amplitudes, as a consequence of their close proximity. During the analysis of the volcanic tremor wave eld at Arenal volcano, Costa Rica, we detected signi cant di erences in the amplitudes of harmonic tremor recorded at the stations of a small-aperture (~210 m) seismic array. The amplitude distributions are geometrically complex and characterized by strong gradients. They occur just for harmonic tremors; any other type of seismic event produces nearly uniform amplitudes across the array. This suggests some relation with harmonic frequency content. Moreover, the spatial amplitude patterns change with time. Some of these observations could be explained by an extreme combination of source, path and site e ects. But they could be also produced by interference of di erent components of the seismic wave eld. We use numerical calculations to investigate the amplitude pattern generated by two interfering plane waves, and are able to reproduce the main features of the observed amplitude patterns. We propose mechanisms that might generate seismic wavefi elds with multiple components and conclude that interference can explain the complexity and variability of the harmonic tremor wave eld at Arenal volcano.
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Bulletin of the Seismological Society of America, Seismological Society of America, 2012, 102 (6), pp.2378-2391
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Javier Almendros, Rafael Abella, Mauricio Mora, Philippe Lesage. Time‐Dependent Spatial Amplitude Patterns of Harmonic Tremor at Arenal Volcano, Costa Rica: Seismic‐Wave Interferences?. Bulletin of the Seismological Society of America, Seismological Society of America, 2012, 102 (6), pp.2378-2391. 〈hal-00763631〉

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