Archive for the ‘the hayward fault’ Category

Loma Prieta plus 25

17 October 2014

Yesterday I attended the Loma Prieta 25 Symposium at the Kaiser Center. It was a quake geek’s Woodstock, where a motley host of experts got together to schmooze, celebrate 25 years of progress since the 1989 earthquake, and look ahead. At 10:16 a.m., along with 27 million other people around the world, we participated in the ShakeOut drill.


Since the Loma Prieta earthquake, Caltrans has finished reinforcing all of the state’s freeway overpasses, EBMUD and Hetch Hetchy have strengthened their principal water mains where they cross the Hayward fault, BART has strengthened its tracks and stations, and PG&E has made huge changes to make the power and gas system more robust. The airports and ports have been upgraded. The big bridges have been fixed or replaced (with only the Golden Gate Bridge upgrade to go).

The work done since Loma Prieta has also made governments work better. The mayor of Napa, Jill Techel, had high praise for the city, county and state emergency service agencies. She said PG&E did a wonderful job during the August earthquake. The federal agency FEMA was on top of things too. And the regional authority ABAG, the main sponsor of the symposium, was charged with energy and ideas to piggyback on the public awareness that followed the Napa quake.

Magnitude-6 events like the Napa earthquake will happen 10 times as often as the “big ones” we’re warned against. Even if the big ones will surely overwhelm some aspect of our preparations, the mitigation and preparedness in place can work wonders with the smaller events like the Napa quake.

The next steps that the experts laid out, the things they want done by Loma Prieta 50, involve increasing the Bay area’s resilience to disasters. Resilience means that people will not just avoid death and injury from a major earthquake, they’ll stay in their homes and return to their jobs quickly. The work of upgrading the infrastructure needs to move beyond the backbones to the limbs and arteries: neighborhood water and gas lines, smaller bridges, individual privately owned buildings. Oakland is ready to begin a program aimed at some 1800 soft-story residences in the city. The state’s earthquake insurance chief and the state senator heading the Insurance Committee were there to describe the advances they want to make in 2015. Progress works this way: inch by inch and year by year.

After Oakland’s Big One, expect a rush of water

8 September 2014

In the days since the South Napa earthquake of 24 August, the people and press appear to be astonished as the local streams have filled with water. The Chronicle published a good summary yesterday. But this always happens with a decent-sized earthquake. It will happen here. You can expect to see this stretch of Arroyo Viejo, in the middle of Hegenberger Expressway, full of freshly released groundwater.


There were widespread reports of this kind in 1857, after the the great Fort Tejon earthquake of 9 January:

On a range of hills, about fifteen miles from the coast, in the district of San Fernando, we understand that a surveying party have discovered quite a large stream making out of the mountain and down a cañon, where, to their knowledge and complete satisfaction, not to say to their sorrow, no water was running or could be found previous to the earthquake. By the letter from Tejón, it will be seen that a similar circumstance occurred in that vicinity. Los Angeles Star, 17 January 1857

Just back of my camp was the dry bed of a stream, where in heavy rains water had at one time run; in this bed two weeks before I had sunk a well some 20 feet hoping to find water, but at that depth the earth was so dry I gave it up as fruitless. Two days after the first or heavy shock a little stream of muddy water was running by my camp which continued to increase each day, until when we moved was quite a little rivulet: no doubt the result of some new fissure in the mountain. Letter of W. E. Greenwell, U.S. Coast Survey, 24 February 1857

The effect upon some of the artesian wells in this neighborhood was remarkable: for a moment the water ceased to flow from the pipes, and then gushed out in greater volume and with more power than usual; we have heard that the channels of other wells, which had become obstructed, and ceased to discharge water, have become re-opened and the subterranean current is now flowing out from the orifice. San Jose Telegraph, 13 January 1857

The water goes away after a few weeks. UCB geologist Michael Manga explained the phenomenon in a talk I attended in May of last year: The shaking settles the bedrock, which in turn forces the groundwater it contains upward. In effect, the rock’s permeability in the vertical direction increases as a result of basement consolidation. This is the same basic mechanism that creates quicksand. Studies after the 1999 Taiwan (Chi-Chi) earthquake showed that this water would be replaced in about 140 years—which is coincidentally the average interval between large quakes on the Hayward fault in the last thousand years. The effect takes place within a rupture length of the fault—that accounts for the response of wells in San Jose to a Southern California earthquake whose rupture ran about 360 kilometers, from Parkfield to Cajon Pass.

Hayward fault slickensides

9 June 2014

Here’s an odd curio that I spotted down in Menlo Park at the U.S. Geological Survey campus. During a trenching study of the Hayward fault up at Point Pinole, the active trace was uncovered and this plaster cast was made. It sits by the entrance of the Map Sales Room in Building 3.


Today we would make a lidar scan of a surface like this to document its slickensides in a precise database. But you have to feel some affection for this low-tech artifact, which presumably has also been scanned to ensure its immortality.


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