ASK A SCIENTIST
Question: Will California eventually fall into the ocean?
Answer: Brittany, you've asked a question that we hear often. I have no idea where the idea comes from that the next "Big One" will cause California to fall into the ocean. It certainly isn't from science.
We now know about plate tectonics and that most earthquakes occur near the edges of these plates. Most of California is on the North American Plate while the southwestern part of California is on the Pacific Plate. The Pacific Plate is moving in a northwesterly direction with respect to the North American Plate at about 5 cm/year (2 inches/year). The boundary between these two plates is the famous San Andreas Fault. This fault is off the coast of northern California but if you traveled south along the fault, you would come on land just north of San Francisco Bay. Traveling farther south you would again be in the ocean just west of the Golden Gate Bridge and then come on land once more just south of San Francisco. This is the section of the fault, which ruptured in 1906 causing the San Francisco Earthquake and fire. The land on opposite sides of the fault moved as much as 16 feet with respect to the other side. This was one of the first earthquakes recorded by seismographs.
As we continue our trip southward along the San Andreas Fault we would eventually find ourselves east of Los Angeles and would travel through the Salton Sea and finally into the Bay of California. The southern section of the San Andreas Fault last ruptured in 1857. Seismologists know that this section could break again at any time. Would this produce the so-called "Big One?" Well, there will not be just one Big One. By digging trenches across the fault and studying the rocks and earth, scientists know that large earthquakes have occurred over and over and will continue to occur.
Even when the next large earthquake occurs, it will still be much smaller than the magnitude 9.0 earthquake in Sumatra, which caused so many deaths due to the tsunami it generated. A California earthquake will not produce a tsunami and probably will not exceed magnitude 8.0 in size which means the ground movement will be one-tenth that of the Sumatra Earthquake. But an earthquake of that size will cause a tremendous amount of damage and loss of life. We do not know how skyscrapers will behave because there has not been an earthquake of this size near an urban area since the building boom of the past half-century.
Will California fall into the ocean? No, but at each earthquake, the land west of the fault moves north. In fact, millions of years ago, the land west of the fault was hundreds of miles farther south. Since Los Angeles is on the Pacific Plate and San Francisco is on the North American Plate, some millions of years in the future, San Francisco and Los Angeles will be adjacent neighbors.
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