What makes an earthquake "significant"?
Events in this list and shown in red on our real-time earthquake map and list are considered “significant events’, and they are determined by a combination of magnitude, number of Did You Feel It responses, and PAGER alert level.
Here is the equation:
mag_significance = magnitude * 100 * (magnitude / 6.5);
pager_significance = red is 2000 : orange is 1000 : yellow is 500 : green is 0;
dyfi_significance = min(num_responses, 1000) * max_cdi / 10;
significance = max(mag_significance, pager_significance) + dyfi_significance;
Any event with a significance > 600 is considered a significant event and appears on the list.