Awaiting the “Big One” Every once in a while there are earthquakes that greatly affect the people in the surrounding areas. To be more specific, Haiti, Chile, Japan, and Northridge come to mind. These places have experienced some of the largest earthquakes in most recent years and millions of people were affected by these quakes alone. Many lost their homes, valued possessions, and even close friends and family members. However, one of the most anticipated quakes in California is drawing closer. Several people are anxiously awaiting the massive rupture that is supposed to occur along the San Andreas Fault within the next few decades. In order to understand more about the inevitable “Big One,” it is important that one learns where the fault lies in California and how it works, how geologists have predicted this, how to prepare for it, and how to stay safe during and after the shaking occurs. Now is the time that Californians need to be aware of the impending shock of another massive earthquake. The location and mechanics of the San Andreas Fault play a large part in understanding what is going to make this earthquake so impactful. This one fault runs along most of California’s coastline “from northern California southward to Cajon Pass near San Bernardino” (Schulz 1). That distance is over 800 miles long and a quake can happen anywhere along it. The fault itself is created by the two plates on either side of it; the Pacific Plate (on the west) and the North American Plate (on the east). For the most part, the two plates are sliding past one another. The Pacific Plate moves northward at about two inches per year relative to the North American Plate (Stoffer 1). This movement is known as a right-lateral strike-slip. However, at some areas of the fault there appears to be a staircase pattern. The staircase pattern is composed of not only strike-slip, but also compressional forces which help shape SCEC website
SCEC website the mountains around us (Stoffer 1). The basic knowledge of the location and movement along the fault can help guide scientists to make sound predictions. Although scientists cannot pinpoint exactly when and where an earthquake will occur, they can use statistics and data from past earthquakes to approximate the timespan in which one will happen and the magnitude of the quake. It is imperative that the years of previous major earthquakes in the region are known. Ragnar Stefansson states that “the length of time between earthquakes is related to regional velocity of strain buildup across plate boundaries” (Stefansson 18). To understand this better, imagine taking two pieces of coarse sand paper and rubbing them together. They certainly do not slide past one another as easily as two pieces of plain paper would. As you continue to apply forces in opposite directions, you will notice that stress is building up. If you continue at this rate, they will eventually slip past one another and release all of the built up energy. As you repeat this, you will notice that (if forces are applied at the same rate) it takes about the same amount of time for them to slip. In terms of the San Andreas Fault, these time intervals in the past have been around 150 years. The last major quake along the fault occurred in 1906 at the San Francisco Bay (106 years ago). However, the last big one to hit the southern region of the San Andreas was in 1857 (Schulz 1). If you calculate that, it was 155 years ago. This means that we are due for a large earthquake in southern California within the next couple of decades. Magnitude is also predicted using past data. Historically, “the San Andreas Fault System has a record of moderate to great earthquakes” (Stoffer 2). The two major earthquakes previously recorded along the fault (the great San Francisco earthquake in 1906 and the great Fort Tejon earthquake in 1857) were roughly the same magnitude; between 7.8 and 8.3 (Stoffer 2). This means that we can expect the next major earthquake