The traditional picture people have in their minds of great earthquakes is of huge cracks opening in the ground, and cars and people and buildings falling in. Some people even think that California will be demolished and fall off into the Pacific Ocean. That may be the wishful thinking of some in middle America, especially in the “red” States, particularly with Berkeley in mind, but I don’t think it will be quite that bad. Let’s look at some facts.

Firstly, the study of the science of Plate Tectonics tells us that the Pacific Plate, which abuts the North American Plate, is moving inexorably in a north-west direction at a rate of about 3-6cm per year. The boundary between the Pacific Plate and the North American Plate runs through the Bay Area, and manifests itself in massive cracks in the earth such as the San Andreas, the Hayward, and the Calaveras faults. These cracks alternately jam up, and then suddenly give way, so that north-west drift is not a nice smooth ride.

The last big quake on the Hayward Fault occurred 140 years ago in 1868, with an estimated magnitude of 7.0. Most of the actual slippage of the Pacific Plate, about four feet, occurred on the southern half of the fault, around Hayward, hence its name. Digging of trenches across the fault line reveals that the part through Berkeley and to the north remains jammed up solid.

Since roads and streets have been built in the last fifty years or so, fault creep has occurred in the southern part, which may have relieved some of the strain. You can see the deformed curbs, sidewalks, and buildings where they straddle the fault. But there is little evidence of fault creep along the section through Berkeley, except across Memorial Stadium, part of which has moved about thirteen inches since it was built in 1923.

Do you see any evidence of the Hayward Fault, or any fault creep in this photo of the playing field in the southern part of Codornices Park? I don’t, none whatsoever. But it runs right through the center of the photograph. I often try to imagine it after the earthquake has wrought its havoc. Not only will we have lost the ball, but possibly a few of the players as well.

The last big earthquake in the Bay Area, Loma Prieta, occurred on October 17, 1989. 69 people were killed, 3757 were injured, and 12,000 people were left homeless. Most of the damage occurred far from the epicenter, which was in an unpopulated area of the Santa Cruz mountains. The Cypress Structure and Bay Bridge collapses were attributed to construction deficiencies, and the Marina District structural failures to liquefaction of fill, not because they were on, or anywhere near the epicenter or the actual fault line.

But in the Santa Cruz mountains, the ground certainly ripped open like a burst zipper, with a sideways movement of about 1.6 meters. Photo courtesy of USGS.

You can see more photos of the zipper effect here.

The previous earthquake comparable to what is likely to happen on the Hayward Fault very soon was the Great San Francisco Earthquake of 1906. Anybody who has not read Simon Winchester’s Book, A Crack in the Edge of the World, should do so at this point, and then take a drive out to Olema in Marin County and look at the evidence. The burst zipper effect can be seen in the fences, roads, and lines of trees displaced by about 8.5 feet. Photo courtesy of USGS.

As with the Loma Prieta earthquake though, and the last Hayward Fault earthquake in 1868, almost nobody lived there at the time. It’s a totally different story for the Hayward Fault today where millions of people live in homes and work in offices built right on top of the fault.

So, to answer the question as to whether the Hayward Fault through Berkeley will rip open like a burst zipper, one has to pose the question, why wouldn’t it? The buildings built on top of it aren’t going to glue it together! The Pacific Plate is moving, like it or not, and the timing points towards any day now. I do not think I am being unnecessarily alarmist. I do think though, that most people who live in the area are being inordinately complacent.

Nobody, even the most knowlegeable seismologist, knows whether the next earthquake on the Hayward Fault will rip open like a zipper, much less where that scenario would occur. But what we know for certain is that the fault, or at least parts of it, did rip open 140 years ago as the ground to the west of the fault shifted northward by about eight feet. And, remember that 140 years is the average interval for the last five quakes on the fault.

The exact location of the fault is not clearly visible, except to the trained eye. It has taken the digging of a number of trenches to pinpoint exactly where it is. The past 50 years of road construction, building, and landscaping have pretty much wiped out all evidence of it. Take a look at the Google Earth image below. If the red line weren’t there, could you see evidence of the fault? You can’t even see it when walking on the ground. Would anybody in their right mind, knowing what we do today, build a tots’  playground right on top of the fault? Well, take a look at the yellow stick pin in the middle of the image.

That’s the tots’ playground in Codornices Park. I don’t believe the City had the intention of building a kiddies’ playground right on top of an earthquake fault. Probably, the exact location of the fault as shown by the red line became clear long after the playground was built. Let’s take a look at the playground as seen on the ground.

Do you see any sign of an active earthquake fault in that picture? It’s probably right under that sandbox at the bottom of the blue slides. That’s my whole point here. Over the years, the evidence of the fault has been so well disguised that most people, particularly the Moms and Dads with their kids at this playground, have no idea it is there. Same with the people who live in the houses that have been built on the fault. Other than the little shakers we get in Berkeley every few months, with a magnitude of about 4.0 on the Richter Magnitude Scale, there is nothing that’s sufficiently in our face to make us be better prepared.

Don’t forget that the Richter scale is logarithmic. What does that mean? It means that a 5.0 is ten times bigger than the little 4.0 tremors that we often feel, and a 6.0 is ten times bigger than a 5.0, and a 7.0 (which is the minimum that seismologists think will occur soon) is ten times bigger than a 6.0. Ten times ten times ten is 1000, which how much bigger a 7.0 is than the little tremors of the past few months.  But it’s actually worse than that, because it is 31,000 times STRONGER, and it’s the STRENGTH of an earthquake that knocks down buildings. Check this out, and use the USGS Calculator to play with some numbers if you really want a sleepless night.