The Big One

There are indications that the San Andreas and related faults have unprecedentedly high stress levels, raising concerns that a 7+ earthquake is due sooner and not later in the area.

Having had been in 2 earthquakes, and remembering one (I was less than 2 years old for the first one), I really hope that is not going to be as bad as it looks.

Earthquakes usually occur along fracture zones in Earth's crust, where large tectonic plates slide past one another and become locked. Stress builds up over long periods and is suddenly released in the form of an earthquake. In Southern California, the San Andreas and San Jacinto faults are among the most significant of these zones, accommodating most of the plate motion in the region.

Where the two fault systems approach each other northeast of Los Angeles lies the Cajon Pass—a tectonically complex junction where a rupture on one fault could potentially cross onto the other. Since the last major earthquake to affect the wider Los Angeles region, the Fort Tejon earthquake of 1857, with a magnitude of 7.9, tectonic stress along the fault segments has built up continuously during a prolonged quiet period that has long concerned researchers, given the potential for a large future rupture.

In a new study led by Dr. Liliane Burkhard of the Division of Space Research and Planetary Sciences (WP) at the Physics Institute of the University of Bern, an international research team modeled 1,000 years of earthquake history along the southern San Andreas and San Jacinto fault systems to estimate the present-day stress loading at Cajon Pass. Researchers from the University of Hawaiʻi at Mānoa, the U.S. Geological Survey Earthquake Science Center in Pasadena, and the Scripps Institution of Oceanography at UC San Diego were involved.

The results show that tectonic stresses in the region have reached and, in some cases, exceeded the highest levels of the last millennium.

In the study, the researchers also introduced the concept of Cajon Pass as an "earthquake gate," a junction that controls whether large earthquakes remain confined to a single fault or propagate across both systems simultaneously. The study has just been published in Journal of Geophysical Research: Solid Earth.

There are indications that stress is high in both the San Andreas and San Jacinto faults, meaning that there is an elevated chance of both faults rupturing at the same time.

Not good, but still better than Donald Trump.