New study on the 1941 Gloria Fault earthquake and tsunami

Abstract

Abstract. The M ∼ 8.3-8.4 25 November 1941 was one of the largest submarine strike-slip earthquakes ever recorded in the Northeast (NE) Atlantic basin. This event occurred along the Eurasia-Nubia plate boundary between the Azores and the Strait of Gibraltar. After the earthquake, the tide stations in the NE Atlantic recorded a small tsunami with maximum amplitudes of 40 cm peak to through in the Azores and Madeira islands. In this study, we present a re-evaluation of the earthquake epicentre location using seismological data not included in previous studies. We invert the tsunami travel times to obtain a preliminary tsunami source location using the backward ray tracing (BRT) technique. We invert the tsunami waveforms to infer the initial sea surface displacement using empirical Green's functions, without prior assumptions about the geometry of the source. The results of the BRT simulation locate the tsunami source quite close to the new epicentre. This fact suggests that the co-seismic deformation of the earthquake induced the tsunami. The waveform inversion of tsunami data favours the conclusion that the earthquake ruptured an approximately 160 km segment of the plate boundary, in the eastern section of the Gloria Fault between −20.249 and −18.630 • E. The results presented here contribute to the evaluation of tsunami hazard in the Northeast Atlantic basin.

Reanalysis of the 1761 transatlantic tsunami

“…(Kaabouben et al, 2009). These two events produce less than one-meter wave height in the North East Atlantic and barely observed wave in the Caribbean Islands (Baptista et al, 2016; …”

“…The code solves linear and non-linear shallow water equations (SWEs) in a Cartesian or spherical reference frame using a system of nested grids and a moving boundary condition to track the shoreline motion based on COMCOT (Cornell Multi-grid Coupled 5 Tsunami Model; Liu et al, 1995;. The code was benchmarked with the analytical tests presented by Synolakis et al (2008) and tested in Miranda et al (2014) and Baptista et al (2016), Wronna et al (2015) and Omira et al (2015).…”

Synthetic tsunami waveform catalogs with kinematic constraints

“…The 1939 earthquake and tsunami had its source close to the Azores, at −24.34 • E, 37.17 • N, on the western tip of the Gloria Fault (Buforn et al, 1988;Reis et al, 2016). The 1941 earthquake and tsunami, one of the largest submarine strike-slip events ever recorded, had its source at −19.04 • E, 37.41 • N, close to the middle of the plate boundary (Udias et al, 1976;Lynnes and Ruff, 1985;Baptista et al, 2016). The 1975 earthquake had its epicentre close to −17.50 • E, 35.90 • N, on the eastern part of the plate boundary, 200 km to the south of Gloria Fault.…”

“…Green circles correspond to deep earthquakes (depth greater than 30 km). Lynnes and Ruff (1985), Baptista et al (2016). b Modified from Lynnes and Ruff (1985) according to the proposed higher rigidity modulus.…”

Answer to Reviewers and Revised Manuscript

“…We assume that the faults are vertical with a maximum width of 40 km. We consider a modulus of rigidity of µ = 5.0 × 10 10 Pa, a seismic coupling coefficient between plate kinematics and earthquake generation χ = 1.0 for all fault segments, and b(β) = 0.98, as estimated by Bird and Kagan (2004) for slow oceanic transform faults. Considering m min = 6.0 we can estimate earthquake activity rate λ.…”