Controls on the T Phase Energy Fluxes Recorded on Juan Fernandez Island by Continental Seismic Wave Paths and Nazca Bathymetry

Abstract

T phases from 54 South American earthquakes with Mw > 5.2 are observed at a broadband station on Juan Fernandez Island. We computed the T phase energy flux (TPEF) values of the seismograms. The TPEF values show a large dispersion that can be explained by considering the tectonic characteristics of the South American plate and the Nazca plate bathymetry. The TPEFs generated by the 2015 Illapel and 2017 Valparaíso seismic sequences were controlled by the positions of the interface events along the dip. The central and downdip interplate earthquakes were more efficient in the generation of T phases than the near‐trench interplate earthquakes (depths of <15 km). The variations in the generation efficiency with depth are explained by the continental raypaths of the body waves and the incidence angles of waves entering the sound fixing and ranging channel. Additionally, we observed differences in the TPEFs from both earthquake sequences that were controlled by seamounts atop the Nazca plate along the T phase paths.

Seismic ocean thermometry

“…T waves propagate largely in the form of the lowest available vertical mode, which has a frequency-dependent structure: High-frequency modes are more narrowly confined to the SOFAR channel axis, whereas low-frequency modes span a substantial portion of the water column (28). T-wave arrivals usually have a high signal-to-noise ratio in a frequency range of 1 to 10 Hz (23,24,30,31). To maximize the sensitivity in the deep ocean, we filter the DGAR T-wave seismograms to the lowest-possible frequency band of 1.5 to 2.5 Hz (Fig.…”

Solving a Seismic Mystery With the Audio From a Diver's Camera: A Case of Shallow Water T‐Waves in the Persian Gulf

“…One must note that apart from the Kish Island where numerous, long tremors were reported likely due to a similar mechanism as described above, no similar signals were documented in the north, that is, Iran. To our knowledge, no broadband stations capable of recording the high‐frequency T ‐waves (>50 Hz) were deployed near the Iranian shorelines at the time of the earthquake and thus comparison of the divers' signal with onland seismic records is not possible (see Sáez & Ruiz, 2018 and Text S17 in Supporting Information ). The two closest Iranian seismic stations to the epicenter (i.e., LAR and LMD; see Text S1 in Supporting Information ) are more than 120 km away along complex elastic paths reaching >2,000 m altitudes.…”

Determining Crustal Attenuation With Seismic T Waves in Southern Africa

“…Single‐station analyses of travel time and polarization are feasible to identify T waves. It was confirmed that T waves can be converted from the S waves via analyses of travel time (Lin, 2001; Sáez & Ruiz, 2018). With these methods, the T‐P and T‐S phases were identified in the Alboran Sea (Carmona et al., 2015).…”

“…The energy of the T phase, generally generated by marine earthquakes, is coupled into the ocean seafloor near the source and converted to seismic waves at the continental slope. The T phase does not depend only on the earthquakes' magnitude, but also on the depth where earthquakes occur, the continental slope, the conversion location, and the conversion efficiency (Carrasco et al, 2019;De Caro et al, 2020;Lin, 2001;Sáez & Ruiz, 2018). Moreover, the mechanism of conversion/coupling is complex, even though model summation (de Groot-Hedlin & Orcutt, 1999, 2001a and ray theory (Chen et al, 2017) 4° to the coast (Buehler & Shearer, 2015), indicating that crustal attenuation structures in the inner stable continent (e.g., >4° from the coast) are difficult to invert with the method proposed in this study.…”

“…However, the types of seismic phases converted from hydro‐acoustic waves are still not well understood. The converted seismic T phases are considered to consist of only P ( T‐P ; Sáez & Ruiz, 2018), only S ( T‐S ; Koyanagi et al., 1995), P and S waves (Carmona et al., 2015; de Groot‐Hedlin & Orcutt, 2001b), Rayleigh ( T ‐Rayleigh; Stevens et al., 2001), and Love ( T ‐Love; de Groot‐Hedlin, 2020).…”