Earthquake **audible only with appropriate speakers**

This is an example of a low-frequency sound often recorded through the hydrophone on the MARS cabled observatory - an earthquake. MARS is located on Smooth Ridge (36.7125N, 122.1869W), west of Monterey Bay at approximately 900 m depth (http://www.mbari.org/at-sea/cabled-observatory/). This magnitude 3.8 earthquake occurred on July 18, 2016 at 05:53:31 UTC (USGS data). It was part of a small earthquake swarm along the San Andreas Fault, approximately 50 miles east of the hydrophone. All quakes in this swarm, with magnitudes as low as 1.9, were detected by the hydrophone. We have recorded as many as 40 earthquakes within a single day. The original recording was normalized, and speed was increased 5X to make the low frequency sound more audible. Still, subwoofer or headphones are recommended.