Analyses of extreme swell events on La Réunion Island from microseismic noise

Abstract

S U M M A R YOcean wave activity excites seismic waves that propagate through the solid earth, known as microseisms, which, once recorded on oceanic islands, can be used to analyse the swell. Here, we analyse the microseismic noise recorded in different period ranges by the permanent seismic station RER on La Réunion Island and by a temporary network of 10 broad-band seismic stations deployed on the island to analyse extreme swell events. We perform a comparative analysis of cyclonic and austral swell events by analysing not only the primary (PM, ∼10-20 s period) and secondary (SM, ∼3-10 s) microseisms but also the long-period secondary microseisms (LPSMs, ∼ 7-10 s), which may result from the interaction between incident ocean waves and the reflected waves off the coast. We compare the microseismic observations with buoy data when available and with hindcasts from numerical ocean wave models. We show that each cyclone is characterized by its own individual signature in the SM, which depends not only on its distance and intensity but also on its dynamics and trajectory. Thus, the SM contains relevant information for cyclone detection and monitoring. Analysing the PM and the LPSM, and comparing it to direct buoy observations and/or wave numerical models allows characterizing the local impact of the swell with the island in terms of amplitude, period, and sometimes, direction of propagation, making possible to use a seismic station as an ocean wave gauge. The microseisms, which link the atmosphere, the ocean and the solid Earth, can thus provide valuable observations on extreme swell events, in addition to oceanic and meteorological data.

Multisensor, Microseismic Observations of a Hurricane Transit Near the ALOHA Cabled Observatory

“…In the 2F microseism band (3-10 s), normally attributed to the interaction of broadly directional waves directly from typhoons, Davy et al (2016) found lower frequency microseisms (7-10 s) attributed to the interaction of a swell with its own coastal reflection (compare with results of Chi et al, 2010, in prior paragraph). In one instance (during Tropical Cyclone Dumille in January 2013), Davy et al (2016) describe the interaction between waves from the nearby Tropical Cyclone Dumille, with waves generated by a distant extra-tropical storm in the Southern Indian ocean. Duennebier et al (2012) suggested that the "background" microseismic level at frequencies below 0.4 Hz at Station ALOHA is (1) uncorrelated to local wind speeds and (2) attributed to the double-frequency microseisms due to incident long period swells interacting with their nearby coastal reflection.…”

“…Davy et al () and Davy et al () show observations of microseisms and ocean swell generated by tropical cyclones around Reunion Island in the Indian Ocean. In the 2F microseism band (3–10 s), normally attributed to the interaction of broadly directional waves directly from typhoons, Davy et al () found lower frequency microseisms (7–10 s) attributed to the interaction of a swell with its own coastal reflection (compare with results of Chi et al, , in prior paragraph). In one instance (during Tropical Cyclone Dumille in January 2013), Davy et al () describe the interaction between waves from the nearby Tropical Cyclone Dumille, with waves generated by a distant extra‐tropical storm in the Southern Indian ocean.…”

“…As there is no clear source of opposing wave energy for the Typhoon Shanshan low-frequency 2F microseisms, it seems reasonable to ascribe an apparent source due to Taiwan coastal reflection or propagation/reflection from the continental shelf of the East China Sea. Davy et al (2014) and Davy et al (2016) show observations of microseisms and ocean swell generated by tropical cyclones around Reunion Island in the Indian Ocean. In the 2F microseism band (3-10 s), normally attributed to the interaction of broadly directional waves directly from typhoons, Davy et al (2016) found lower frequency microseisms (7-10 s) attributed to the interaction of a swell with its own coastal reflection (compare with results of Chi et al, 2010, in prior paragraph).…”

A New Coupled Ocean‐Waves‐Atmosphere Model Designed for Tropical Storm Studies: Example of Tropical Cyclone Bejisa (2013–2014) in the South‐West Indian Ocean

“…Since the oceanic waves also propagate to the north, behind the cyclone, the southern side of La Réunion is impacted by the swell several hours after the passage of the cyclone (Figure f). Analyzing the microseismic noise using permanent and nonpermanent seismic stations, Davy et al () showed that microseismic noise was still giving a recordable signal when Bejisa was located south of the island confirming the presence of northward swell after the passage of the TC.…”

A Feasibility Study on Monitoring Crustal Structure Variations by Direct Comparison of Surface Wave Dispersion Curves from Ambient Seismic Noise

“…We observe that the secondary microseism noise level is minimum during local summer, with higher levels occurring during local winter when the Southern Ocean experiences violent winter storms. The relatively higher secondary microseisms in austral winter could also be explained by instances of icebreakups and near-coastal interactions related to iceberg reflections (Grob et al 2011;Davy et al 2016;Pratt et al 2017;Lepore & Grad 2018). For the primary microseism band, noise levels are reduced in the austral winter.…”