4 ms·

I'm a non-Californian, so I'm not very familiar with the tectonics at play here. If there's an earthquake on this fault, how bad would it be? Would it trigger

I'm a non-Californian, so I'm not very familiar with the tectonics at play here. If there's an earthquake on this fault, how bad would it be? Would it trigger a tsunami? Would SF and LA be damaged? Could this cause "the big one" that gets mentioned occasionally? How bad would such a quake be?

monkburger 3y ago
San Andreas is a transform fault, also known as a 'strike-slip' fault. These generally do not cause as much damage as a subduction zone event, also known as dip-slip. An example of this type of event (dip-slip) would be the 2004 Indian Ocean earthquake, or the violent 1700 Cascadia Megathrust Earthquake. Personally, Cascadia is /more/ dangerous than any strike-slip earthquakes like SA. We have sedimentation records of massive Cascadia tsunamis going back to about ~900CE.
inference-lord 3y ago
One thing which isn't discussed enough is how bad the Tsunami is environmentally. The coastline of Japan is absolutely littered with crap from the 2011 Tsunami. All manner of chemicals were sucked into the nearby sea, tires, carpets, hard and soft plastics, absolutely everywhere. It almost looks unrecoverable. I know that seems like a non-issue in the grand scale of things, but Tsunami's of the past didn't do this. Most pollution was biodegradable. I can't imagine what the coast of LA would look like after a similar event :(
- monkburger 3y ago
  More of a concern in the bay area, the geological composition is sand, mud, basic river delta sediments--not the most stable stuff. eg: During a hypothetical Earthquake in the Bay area, the liquefaction of sand occurs, which causes underground structures to move upward due to buoyancy (think of a lower level parking garage), and the soil mass from the structure collapses. the liquefied sand diffuses to the surrounding area after the earthquake, causing the sand beneath the underground structure to be lost, and the building will return to its original position or even collapse.
  - inference-lord 3y ago
    Yeah, also quite bad, I've seen the aftermath of this liquefaction in Japan. Whole apartment blocks topped over with seemingly good foundations.
dredmorbius 3y ago
The Parkfield region is very sparsely populated. A disruption on this segment of the San Andreas Fault, comparable to past similarly-sized events, would probably NOT have significant effects in major populated regions of either the San Francisco Bay Area (San Jose is 128 miles north) or Southern California (Santa Barbara, which is the northernmost extant of the SoCal conurbanation is 110 miles south). That's roughly 120 and 180 km respectively. Earthquakes' effects are most strongly felt immediately around the epicenter, and diminishes with the square of the distance. The San Andreas Fault, being a strike-slip fault (plates moving laterally against one another) and lying principally inland has very low tsunami risk. Tsunami are most associated with superthrust faults, in which one plate rides up over another, and energy is release with a strong vertical displacement, as with the 2011 Tohoku and 2004 Indian Ocean earthquakes.

monkburger 3y ago

San Andreas is a transform fault, also known as a 'strike-slip' fault. These generally do not cause as much damage as a subduction zone event, also known as dip-slip. An example of this type of event (dip-slip) would be the 2004 Indian Ocean earthquake, or the violent 1700 Cascadia Megathrust Earthquake. Personally, Cascadia is /more/ dangerous than any strike-slip earthquakes like SA. We have sedimentation records of massive Cascadia tsunamis going back to about ~900CE.

inference-lord 3y ago

One thing which isn't discussed enough is how bad the Tsunami is environmentally. The coastline of Japan is absolutely littered with crap from the 2011 Tsunami. All manner of chemicals were sucked into the nearby sea, tires, carpets, hard and soft plastics, absolutely everywhere. It almost looks unrecoverable. I know that seems like a non-issue in the grand scale of things, but Tsunami's of the past didn't do this. Most pollution was biodegradable. I can't imagine what the coast of LA would look like after a similar event :(

monkburger 3y ago
More of a concern in the bay area, the geological composition is sand, mud, basic river delta sediments--not the most stable stuff. eg: During a hypothetical Earthquake in the Bay area, the liquefaction of sand occurs, which causes underground structures to move upward due to buoyancy (think of a lower level parking garage), and the soil mass from the structure collapses. the liquefied sand diffuses to the surrounding area after the earthquake, causing the sand beneath the underground structure to be lost, and the building will return to its original position or even collapse.
- inference-lord 3y ago
  Yeah, also quite bad, I've seen the aftermath of this liquefaction in Japan. Whole apartment blocks topped over with seemingly good foundations.

dredmorbius 3y ago

The Parkfield region is very sparsely populated. A disruption on this segment of the San Andreas Fault, comparable to past similarly-sized events, would probably NOT have significant effects in major populated regions of either the San Francisco Bay Area (San Jose is 128 miles north) or Southern California (Santa Barbara, which is the northernmost extant of the SoCal conurbanation is 110 miles south). That's roughly 120 and 180 km respectively. Earthquakes' effects are most strongly felt immediately around the epicenter, and diminishes with the square of the distance. The San Andreas Fault, being a strike-slip fault (plates moving laterally against one another) and lying principally inland has very low tsunami risk. Tsunami are most associated with superthrust faults, in which one plate rides up over another, and energy is release with a strong vertical displacement, as with the 2011 Tohoku and 2004 Indian Ocean earthquakes.