Seismic tremor at the 9°50′N East Pacific Rise eruption site

Abstract

[1] Ocean bottom seismic observations within the 9°50 0 N region of the East Pacific Rise indicate persistent, low-amplitude tremor activity throughout the October 2003 through February 2007 period of monitoring. These signals exhibit either monochromatic or polychromatic spectral characteristics, with a $6 Hz fundamental frequency and up to two harmonics. Individual events cannot be correlated between nearby (<1 km) stations, implying the presence of multiple, small-amplitude sources positioned within the shallow crust. Tremor exhibits a semidiurnal periodicity, with some stations recording activity during times of increasing tidal extension and others detecting tremor signals during times of increasing compression. The amplitude, duration, and rate of activity also correlate positively with fortnightly changes in the amplitude of the tides. These spatiotemporal patterns are consistent with tremor generation in response to tidally modulated fluid flow within a network of shallow cracks. Tremor energy flux is spatially and temporally heterogeneous; however, there are extended periods of greater and lesser activity that can be tracked across portions of the array. Despite their shallow crustal origin, changes in tremor amplitude and spectral character occur in the months prior to a major microearthquake swarm and inferred seafloor spreading event on 22 January 2006, with an increase in the degree of correlation between tremor activity and tidal strain in the weeks leading up to this event. After the spreading event, two eruption-surviving stations near the axis continue to show high rates of tremor activity, whereas these signals are suppressed at the single station recovered from the near-axis flanks. This off-axis quiescence may result from the dikeinduced closing of cracks or perhaps from the emplacement of impermeable flows near the station.

Seismicity and Noise Recorded by Passive Seismic Monitoring of Drilling Operations Offshore the Eastern Canary Islands

“…Occurrence of harmonic tremors similar to those observed in this work has been reported in other volcanic and non-volcanic regions of the world, e.g., Pontoise and Hello (2002) offshore Ecuador, Tolstoy et al (2002) near Axial volcano on the Juan de Fuca Ridge, Díaz et al (2007) at the Galicia Margin, Monigle et al (2009) at the 9º50' East Pacific Rise, Bazin et al (2010) in Guadeloupe, French West Indies, and Franek et al (2014) in the SW Barents Sea margin. Several hypotheses have been proposed, as discussed later, to explain their origin.…”

“…The harmonic tremors reported in other regions (e.g., Pontoise and Hello, 2002;Tolstoy et al, 2002;Díaz et al, 2007;Monigle et al, 2009;Bazin et al, 2010;Franek et al, 2014) have been associated with gas venting and/or resonance of fluid-filled cracks. The geological setting of the Canary Channel would support an interpretation of the harmonic tremors in terms of resonant vibrations associated with gas seepage.…”

First In Situ Seismic Record of Spreading Events at the Ultraslow Spreading Southwest Indian Ridge

“…Tidally modulated tremor has been found at other hydrothermal systems. Monigle et al () found comparable harmonic tremor at OBS on the East Pacific Rise that was attributed to hydrothermal flow in cracks close to the OBS. There, too, tremor pattern changed in connection with a magmatic event.…”

Origin and Periodic Behavior of Short Duration Signals Recorded by Seismometers at Vestnesa Ridge, an Active Seepage Site on the West-Svalbard Continental Margin

“…Ocean-bottom seismometers (OBSs) are usually deployed in marine settings to investigate local seismicity of an area by monitoring earthquakes (e.g., Grevemeyer et al, 2015;Meier et al, 2021) or long-duration tremors (e.g., Monigle et al, 2009;Hsu et al, 2013;Franek et al, 2014).…”