Does Deep Tectonic Tremor Occur in the Central‐Eastern Mediterranean Basin?

• Published in: Journal of geophysical research. Solid earth 2021-01, Vol.126 (1), p.n/a
• Main Authors: Bocchini, G. M., Martínez‐Garzón, P., Harrington, R. M., Bohnhoff, M.
• Format: Article
• Language: English
• Subjects: ambient tremor; Mediterranean basin; subduction zones; tectonic tremor; transform faults; triggered tremor
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2020JB020448

Tectonic tremor has been observed at the roots of many fault systems around the Pacific rim, including convergent and transform plate boundaries. The extent to which deep tremor signals are prevalent along fault systems elsewhere, including the Mediterranean basin, has not yet been documented in detail. A body of evidence suggests that tremor triggered during the surface waves of teleseismic events may commonly occur where ambient tremor during episodic tremor and slip episodes occur, suggesting triggered tremor provides a useful tool to identify regions with ambient tremor. We perform a systematic search of triggered tremor associated with large teleseismic events between 2010 and 2020 at four major fault systems within the central‐eastern Mediterranean basin, namely the Hellenic and Calabrian subduction zones, and the North Anatolian and Kefalonia transform faults. In addition, we search for ambient tremor during a slow slip event in the eastern Sea of Marmara along a secondary branch of the North Anatolian Fault, and two slow slip events beneath western Peloponnese (Hellenic Subduction Zone). We find no unambiguous evidence for deep triggered tremor, nor ambient tremor. The absence of triggered tremor at the Hellenic and Calabrian subduction zones supports an interpretation of less favorable conditions for tremorgenesis in the presence of old and cold slabs. The absence of tremor along the transform faults may be due to an absence of the conditions commonly promoting tremorgenesis in such settings, including high‐fluid pressures and low‐differential stresses between the down‐dip limit of the seismogenic layer and the continental Moho. Plain Language Summary The discovery of slow earthquakes, or events with rupture velocities intermediate between traditional earthquakes and plate convergence rates, has revolutionized our understanding of the modes of stress release during the seismic cycle, and has implications for seismic hazard assessment. Here, we focus on a specific group of slow, low‐amplitude earthquakes with energy concentrated in the 2–8 Hz frequency range that accommodate slip on faults where rock deformation transitions from brittle to plastic, namely tectonic tremor. To date, tectonic tremor is best documented primarily in fault systems along the Pacific rim. Whether the absence (or infrequent occurrence) of tremor outside of the Pacific rim is due to a sampling bias or due to non favorable physical conditions is still poorly understood. We pe