There are generally two types of hay bales. With quite different weights. The most common ones that people buy at feed stores or the farmer, and can be moved by one person, are the type you may have bucked into the barn for your uncle who had a farm when you were a teenager. They are around 3-4 feet long by 24x18 inches square.
How Earthquakes Happen. An aerial view of the San Andreas fault in the Carrizo Plain, Central California. An earthquake is the vibration, sometimes violent, of the Earth's surface that follows a release of energy in the Earth's crust. This energy can be generated by a sudden dislocation of segments of the crust, by a volcanic eruption, or event by manmade explosions.
When the frictional forces are overcome, the plates slip suddenly and shallow focus earthquakes are generated. Landscape and manmade features (eg rivers, fences and roads) are displaced across the fault as movement occurs. San Francisco has historically suffered significant earthquakes, notably in 1906 and 1989. The average rate of movement along the San Andreas Fault is between 30mm and 50mm per year over the last 10 million years. If current rates of movement are maintained Los Angeles will be adjacent to San Francisco in approximately 20 million years.