I signed up years and years ago for email alerts/notifications from the USGS whenever there was an earthquake anywhere around the world. You can set the sensitivity of these quakes, because, there are literally hundreds of tremblors of varying degrees around the planet each day, so I set my sensitivity scale to only send me alerts/updates whenever there is a 5.5 or larger quake somewhere. Since this mornings first quake near Japan, which registered a 7.8, and including the 8.9, there have been 54 (and counting) aftershocks registering more than 5.5.
I used to have it set for anything above a 4.0, until the quake in Indonesia, and at that time I recall I had over 175 email alerts over about a three day period, so I changed it to 5.5.
EDIT: In the time I took me to post this....56 and counting.