D – 1 An External Source Of Earthquake Triggering Pressure On The Earth’s Crust
As the following drawing shows, the Gravity Point is the location on the surface of the Earth where the combined gravitational pulls of the sun and the moon are strongest.
As the Earth rotates each day on its North and South Pole axis, its crust on the side which is rotating towards the Gravity Point is accelerated by the sun and moon gravity while the side moving away from the Gravity Point is decelerated or slowed. That creates strain within the crust. And earthquakes are triggered at locations where that strain causes the crust to be bent, stretched, or compressed in just the right directions.
D – 2 An Internal Source Of Earthquake Triggering Pressure On The Earth’s Crust
As that previous drawing shows, once each month the Earth and the moon rotate around a sun – Earth – moon barycenter or center of mass which is a certain distance down beneath the surface of the Earth. The location of that barycenter is constantly moving towards and away from the center of the Earth depending upon the location of the sun relative to the moon. And it is constantly moving around the location of a line drawn between the center of the Earth and the center of the moon.
The solidified iron believed to be the major component of the Earth’s core is roughly 5 times as heavy or dense as the material in the Earth’s crust. As both the core and the crust rotate around that barycenter once each month the mass of the Earth in general attempts to assume the shape of an egg with its ends pointing away from the barycenter. And the solid core tries to move in a direction almost directly away from both that barycenter and from the location of the moon.
The Earth’s gravity, rotation, and its somewhat rigid structure prevent it from undergoing rapid, appreciable changes in shape. And the core is kept from moving within the Earth by those factors. That results in the solid core exerting earthquake triggering pressure at different locations or pressure points in the crust from inside the Earth. Where those pressure points are located is determined by factors such as the location of center of mass of the core relative to the sun – Earth – moon rotation barycenter and the rotational orientation of the Earth as it revolves once each day on its North and South Pole axis.
How Earthquake Sensitives Predict Earthquakes, GeoMonitor: Earthquake Prediction News; April, 1996
Breathing of the seafloor: Tidal correlations of seismicity at Axial volcano, Geology; June 2002; v. 30; no. 6; p. 503-506 (See especially Figure 4A.) (Also, that paper contains a helpful list of references.)
‘Restless Earth’ May Give Advance Notice Of Large Earthquakes (NASA News)
Prediction of Destructive Earthquake by the MDCB-Method, Wang, Wen-xiang and Yang, Wu-yang, Xian Sub-Institute, Coal Science Research Institute of China MDCB Web Site
Earthquake Triggering Processes
Earthquake Forecasting Resources Web Page
Earthquake Triggering Data For 1990 Through 2005, Wave Charts, Earthquake Data Fingerprints