Parkfield, California is a quiet, dusty farming town nestled among rolling hills about midway between Fresno and Monterey. It’s known as the earthquake capital of the world. This is not because there are so many earthquakes there, although there are, but because it has one of the highest densities of seismic technology anywhere. Parkfield has shaken with 6.0-magnitude quakes regularly, roughly every 22 years, and remains the heart of one of the most seismically active areas in California, if not anywhere. (And for what it’s worth, Petrolia, California has the most earthquakes).

The reason for the town’s unusual seismic activity is very simple: it sits directly on top of the San Andreas Fault, the best known, and one of the most active faults in the world. In the Parkfield area, the San Andreas Fault is constantly shifting—millimeter by millimeter, day by day. This continuous movement is unique to the region, as the fault remains relatively locked in both the northern section around San Francisco and the southern section near Palmdale. While the fault in these other areas stays immobile, the central part near Parkfield steadily creeps, creating a contrast that puts pressure on the locked sections to the north and south.

Parkfield’s main strip, stretching just a quarter mile, hosts a small collection of buildings, including a one-room elementary school, the USGS-Berkeley earthquake monitoring site, a Cal Fire station, and the Parkfield Cafe and Lodge. Outside the cafe, a row of mismatched mailboxes serves the dozen or so homes scattered along a few dirt roads branching off the main street. Parkfield might be a small, obscure town to most Californians, but to geologists fascinated by the workings of the Earth, it’s the epicenter of seismic research.

Every hillside and valley, grassy nook and riverbed is home to some kind of instrument that measures earthquakes. Over the years, these instruments have become more sophisticated and expensive, making it necessary in many cases to fence them off with the threat of arrest.  These instruments monitor, hour by hour, or better, millisecond by millisecond, the stirrings of the earth. To geologists, it is ground zero for seismic measurement. 

The town is proud of its reputation. A water tower boasts the tourism slogan: BE HERE WHEN IT HAPPENS (see photo). There is also an iron bridge in the town that has the distinction of standing astride the San Andreas Fault. One one side of the creek that runs beneath the bridge is the North American tectonic plate. On the other is the Pacific tectonic plate. Those two plates are moving south and north respectively at a rate of about 2 inches a year. As we all know, that movement creates immense pressure as the two plates seem otherwise locked in place. That pressure will have to be released at some point. It always has. When that happens, we can expect a potentially devastating earthquake that will rock the state from top to bottom. 

The writer Simon Winchester calls the fault an “ever-evolving giant that slumbers lightly under the earth’s surface and stirs, dangerously and often, according to its own whims and its own rules.” 

Since 1985, a focused earthquake prediction experiment has been in progress in Parkfield. Known as “The Parkfield Experiment“, the project’s stated purpose is to “better understand the physics of earthquakes — what actually happens on the fault and in the surrounding region before, during and after an earthquake.”

Since the mid-1980s, scientists have deployed an array of advanced monitoring devices, including seismometers, strainmeters, creepmeters, and GPS sensors, to capture detailed data on ground movement and strain accumulation. These instruments are designed to measure subtle changes in the Earth’s crust, helping researchers predict seismic events and understand the processes leading up to an earthquake. By continuously collecting data, the experiment has provided valuable insights into the mechanics of fault movement and the potential for earthquake prediction.

Experts also once bored a 10,000-foot-deep hole into the ground in Parkfield, into which they placed a large array of sensors to measure the earth’s movements. The goal of the $300 million project, called the San Andreas Fault Observatory at Depth, or SAFOD, was to allow scientists to study how faults work and how earthquakes happen. The drilling stopped in 2007, but Parkfield remains a hot spot for geologic research.

Parkfield remains critical to better understanding seismic dangers in California. The fault zone is poorly understood at depth and so far, the predictability of earthquakes in the near term is pretty limited. But devices like these could help improve prediction, especially if there is a large quake. But that’s the rub, really. We need to experience a large earthquake to get the best data to know how to predict later ones. So it is in California.