I was in the USAF on Mindanao in 1970-71 operating seismic equipment and analyzing the seismic data (to detect nuclear explosions). Mindanao is a hyper-active seismic area and part of the horseshoe-shaped mega-fault that goes from New Zealand north through Japan/Korea, across the Aleutian Islands, then down the west coast of North and South America. [In 1972-73 I was in northern Thailand, again along the fault line and very close to the epicenter of the Burmese quake described in this post.]
Mindanao experienced significant earthquakes every couple of weeks, including a few strong enough to topple over our equipment racks. Including minor quakes, Mindanao experienced over 400 earthquakes in the 12 months I was there.
And every time we had a big quake, there would be another big quake somewhere else along that horseshoe-fault. Maybe in Alaska, maybe Chile, etc. But entirely predictable.
Why?
Envision a pot of vigorously boiling water. Put a lid on that pot. The boiling water's pressure will force some part of that lid to chatter (foreshock), then lift. The lid will chatter a bit more (aftershocks), and then the lid's weight will slam that lid back down. But the boiling water's pressure still seeks relief. So, the pressure will then force some other part of the lid to chatter, lift and chatter - again to relieve the pressure. Only way to stop this cyclic process is to reduce the pressure. Turn down the stove burner. Or, in the case of our planet, enough earthquakes will reduce the pressure to stop the process...but only until the pressure builds again.
That's exactly what is happening with major earthquakes. Those quakes are the slow relief of pressure along the mega-fault line.
Our USAF seismic training detachment was at Rocky Mountain Arsenal north of Denver's old airport (Stapleton). RMA was also the site of Shell chemical plants whose job was to process WW I, WW II and Viet Nam era
mustard gas, napalm, white phosphorus, lewisite, chlorine gas and sarin gas into inert liquids. Shell then pumped those inert liquids into 10,000-foot holes in the ground at RMA. Every time Shell pumped those liquids into the ground, Denver experienced minor earthquakes. In essence, those gasses were lubricating the faults and causing frequent, minor quakes. At the same time, those minor quakes served to relieve enough pressure to preclude larger quakes.
For more than two decades no one connected the dots between Shell and the quakes. Why? Because no one knew what Shell was doing. Shell's mission was classified....the locals were clueless. But my group connected those dots and ultimately caused a dialog to begin between DoD and the State of Colorado.
A similar set of cause-and-effect quakes occurred in the western San Fernando Valley (Canoga Park) where the DoD jet engine contractor Rocketdyne was located. Rocketdyne would periodically pump toxic fluids into the ground (rejected, stale or excess rocket fuel we suspected). I mean, that part of California sat on the mega-fault, and didn't need any help from Rocketdyne. But...
We were ordered to wear gas masks whenever we were at RMA. And no one had to compel us to do that. I spent about 8 months at RMA, and wearing those masks in the hot summer or very cold winter was unpleasant. Also, we used to joke that RMA's toxicity caused the jackrabbits to grow to 5' tall and glow at night.