An Earthquake Lasted 50 Days, But No One Felt It. Here’s Why
In Cascadia, for example, slow slip events registering as magnitude 6.0 quakes can last two or three weeks and can repeat every 15 months, on average. There is a chance that slow slip events are driven by strange mechanical properties of fault material that we simply don’t yet understand. The International Ocean Discovery Program has also drilled into the subduction zone there to directly sample the sediments involved with these slow slip events, while also sending seismic waves through the region to better map out the fault networks there.
Source: www.nationalgeographic.com