Séminaire ISTerre

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Tracking Tremor & Tremor-like Signals in California

vendredi 27 novembre 2020 - 11h00

Asaf Inbal  - Tel Aviv University, Israel
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Tectonic tremors form a class of tectonic events associated with emergent, long‐duration, low‐amplitude seismic signals whose characteristics are distinct from regular earthquakes, or from the harmonic tremor observed near volcanos. They are sometimes described as resulting from a sequence of Low-Frequency Earthquakes (LFEs), which are essentially short-duration events whose high-frequency content is depleted relative to regular earthquakes of the same size. Efforts for identifying and determining tremor locations are complicated by the fact that tremor signals are similar in many respects to those generated by anthropogenic sources such as vehicle traffic, machinery, or wind farms. This issue may be addressed by using dense seismic array analysis. Due to their configuration (sensor spacing<100 m, aperture 1-10 km), dense arrays can effectively increase the signal-to-noise ratio, and filter low-incidence surface waves. The arrays are therefore capable of detecting low amplitude tremor signals in the 1 to 10 Hz frequency range, even in noisy environments. In the first part of the talk I will discuss array-based methods for discriminating tremor from man-made noise. I will point to the weaknesses and strengths of conventional tremor detection techniques, and discuss the implications for earthquake detection in noisy urban environments. In the second part I will present results from a short-term deployment of a dense array near the Cholame section of the San Andreas Fault. The experiment captured an unusually large tectonic transient that occurred on August 2018, during which tremor was observed to propagate along the Cholame and Parkfield sections. I will discuss the tremor migration patterns resolved by Cholame arrays and the regional network, the relation between tremor and LFE activity, and the frequency-dependent features of the tremor source.

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Equipe organisatrice : Ondes et structures

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