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InSight in ATLO with back shellOn Earth, to record an earthquake a sensor measures the difference between a wave that travels through the planet and a wave that travels along the surface. With multiple sensors and very accurate clocks one can calculate the epicenter of the earthquake in terms of latitude, longitude and (in the last couple of years) depth. For most weaker earthquakes, say Richter 5.4 or lower, any damage to buildings, bridges and roads will usually be very close to the epicenter. An industrious geologist might go out and survey actual earth movements which can horizontal, vertical or both. The problem on Earth is that more powerful earthquakes have two effects: there are aftershocks  (which leads to a long and contentious discussion about what is an aftershock as opposed to an independent earthquake) and damage can be widespread. For example, on October 17, 1989 at 5:04 PM just before a Major League Baseball World Series game between the San Francisco Giants and the Oakland Athletics a magnitude 6.9 earthquake hit the San Francisco Bay Area. It killed 67 people; injured 3,757 and caused more than $5 billion in damage. Some of the more spectacular damage occurred in the San Francisco marina District, the Cypress Freeway and the Oakland Bay Bridge – all about 60 miles northwest of the epicenter. Twelve miles southeast of the epicenter more than 30 percent of Watsonville’s downtown and 1 in 8 houses were destroyed. It would likely be useful to attempt to determine where damage occurred on Mars if there is a suitably powerful Marsquake.

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