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Paul Byrne
@theplanetaryguy.com

Today's 6.98 Mw earthquake was along the Mendocino fracture zone, where the North American, Pacific, and Gorda tectonic plates meet. Per the USGS, the quake took place along a steeply dipping thrust at a depth of 600 m—hence the tsunami alert, which has now been lifted.

Paul Byrne
@theplanetaryguy.com

This kind of quake is not uncommon, and is a testament to the fact that we live on a geologically active world. Thrust-fault-driven quakes generally are common in areas such as this, where one plate subducts beneath another. Indeed, subduction zones host the very largest quakes.

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Paul Byrne
@theplanetaryguy.com

Correction: the fault plane was likely steeply dipping, but the dominant fault motion was strike-slip (with a little dip-slip component, which is fairly usual). So, strike-slip faulting, either mainly north–south or east–west.