The underwater sound of an earthquake at the Main Endeavour Hydrothermal Vent Field

Brendan Smith – brendan.smith@dal.ca
Twitter: @bsmithacoustics
Instagram: @brendanthehuman
Dalhousie University
Department of Oceanography
Halifax, Nova Scotia B3H 4R2
Canada

Additional author:
Dr. David Barclay

Popular version of 1aAO4 – Passive acoustic monitoring of a major seismic event at the Main Endeavour Hydrothermal Vent Field
Presented at the 187th ASA Meeting
Read the abstract at https://eppro01.ativ.me/appinfo.php?page=IntHtml&project=ASAFALL24&id=3770227&server=eppro01.ativ.me

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

The Main Endeavour Hydrothermal Vent Field (MEF) is located on the Juan de Fuca Ridge in the Northeast Pacific Ocean. This ridge is a seafloor spreading center, where tectonic plates pull apart and new oceanic crust is formed as magma upwells from beneath the earth’s surface. This movement of the earth’s crust causes cracks to form, allowing seawater to penetrate downwards towards the magma below, where it circulates and eventually resurfaces into the ocean at temperatures over 300 degrees Celsius. Uniquely adapted organisms thrive at these sites, surviving from energy provided not by the sun, but by the heat and chemical composition of the vent fluid.

Figure 1: Black-smoker hydrothermal vent chimney at the Main Endeavour Hydrothermal Vent Field (Image courtesy of Ocean Networks Canada)

Long term measurements of hydrothermal vent activity are of scientific interest. However, the high temperatures and caustic chemical characteristics make it challenging to place probes directly in the vent flow. For this reason, passive acoustics (listening) can be a useful tool for hydrothermal vent monitoring, because the hydrophones (underwater microphones) can be located a safe distance from the vent fluid. Ocean Networks Canada have had a hydrophone at MEF continuously recording for over 5 years, and for the past year, a 4-element hydrophone array has been recording at this location.

The motion of the tectonic plates in these regions causes a lot of seismic activity, such as earthquakes. On March 6, 2024, a large ~4.1 magnitude earthquake was recorded at MEF, and earthquake rates were the highest observed since 2005. This earthquake was recorded on the hydrophone array and can be seen in the spectrogram in Figure 2.

Figure 2: Spectrogram of ~4.1 magnitude earthquake at MEF

Figure 3 shows differences in the soundscape at Endeavour before, during, and after the earthquake. The changes after the earthquake persist more than 1-week following the event. The duration and higher frequency components of the changes in the soundscape suggest sources other than seismicity.

Figure 3: Acoustic spectra before, during, and after the earthquake at MEF

The hydrophone array also provides us with the opportunity to gain further insights. For example, surface wind/wave-generated noise is a predominant source of ambient sound in the ocean, and the coherence, or spatial relationship between multiple hydrophone elements in the presence of this sound source, is well known. We can compare the measured coherence with the expected (modeled) coherence to explore any deviations, which could be attributed to hydrothermal vent activity. In Figure 4 we see differences between the measurements and model below 1 kHz (outlined by black boxes), suggesting the influence of hydrothermal vent sounds on the local soundscape.

Figure 4: Measured and modeled acoustic vertical coherence at MEF

In conclusion, passive acoustic monitoring can be used to monitor changes in hydrothermal vent fields in response to seismic activity. This earthquake provided a test case to prepare for a more major seismic event, which is expected to occur at Endeavour in the coming years. Passive acoustic monitoring will be an important tool to document vent field activity during this future event.