The San Andreas Fault, the major fault line running through California, is expected to be the source for the "Big One". It has on average a major earthquake every 150 years, but the southernmost segment has not had one since 1680, over 300 years ago (Figure 1). This is why scientists believe that a major earthquake is overdue.
The message is that earthquakes are expected in Southern California, and large ones can cause cause wide spread damage . Preparations are required to not only survive them, but to recover from them as quickly as possible (e.g. weeks instead of months).
Although the focus of this Technical Bulletin is on the recovery of water supplies after a large temblor, all facets of life will be affected by a major earthquake. Proper advanced planning, however, can save lives and hasten the return of services to our communities.
The U.S. Geological Survey (USGS) is leading an effort along with the California Institute of Technology (Caltech) and others to create a hypothetical but possible earthquake scenario for a magnitude 7.8 temblor on the southern portion of the San Andreas Fault. If this massive earthquake hits, it is expected to cause loss of life and serious injuries. It will also cause major damage to lifelines that cross the fault or are affected by the intense shaking, including water and sewer lines, petroleum pipelines, fiber optics cables, bridges, buildings, dams, overhead transmission lines, roads and railways.
Even though Los Angeles is 60 miles from the San Andreas Fault, because it sits on a deep basin of sediments (which gives us our good groundwater aquifers), it will shake like a bowl of gelatin and the ground could shift up and down from 10 to 20 feet, causing severe damage to structures. Modeling of expected ground shaking shows how the shock waves will resonate from the epicenter near Palm Springs into the Los Angeles area (Figure 2).
Figure 2 - Modeled ground shaking after 60 seconds (above), 90 seconds (middle), and 120 seconds (bottom) of a M7.8 earthquake on the San Andreas Fault originating near Palm Springs and moving northwest
The result of the USGS/Caltech work will be a document that describes the expected effects of the earthquake. A detailed report is expected in Spring 2008 leading up to an area-wide disaster drill on November 13, 2008 at 10:00 am (simulated day and time that the "Big One" hits).
As part of the scenario work, the USGS and Caltech convened a panel of water supply experts on July 31, 2007, to determine the potential effects that the major earthquake will have on water supplies. Members from the Water Replenishment District of Southern California (WRD), the Metropolitan Water District of Southern California (Met), Los Angeles Department of Water and Power (LADWP), and others participated in the half-day session. The panel was asked questions about what infrastructure was in jeopardy (pipelines, water tanks, wells, aqueducts, reservoirs), how the damage would be assessed, how repairs would be conducted, how long water supply outages would occur, and where emergency water supply sources could be obtained. Some of the conclusions were:
To paraphrase one panelist, "The groundwater basins are our savings account and can help us get by during this emergency. They can be tapped to make up the water shortages when imported supplies are unavailable." Met agreed and will request that groundwater users take more during an emergency to reduce the imported demand.
To prepare for these emergencies, the groundwater basins should be fully utilized as underground reservoirs and the overlying users prepared to tap into these reservoirs. Water wells should be maintained and have the ability to pump excess capacity. Interconnections should be made with adjacent municipalities to provide water distribution redundancy so that water can be re-routed if one community's system fails. Available aquifer storage space should be utilized. Emergency pumping ordinances should be in place to allow additional pumping in adjudicated basins.
Another study underway by the USGS is looking at how the Central and West Coast groundwater basins can be utilized in such an emergency. They are using computer models to assess land subsidence and seawater intrusion implications for over pumping the basins on a short term basis to provide the water needed during an imported water outage. The results of this two-year study are due in 2008.
"Dare to Prepare" is the slogan being used for the earthquake scenario, and those of us in the water supply business have the responsibility to prepare in order to quickly and properly respond in the aftermath of "The Big One".
Additional information on the "Southern Andreas Fault Earthquake Scenario" can be obtained by contacting the author, or from scenario managers Dale Cox of USGS at firstname.lastname@example.org, or Keith Porter of Caltech at email@example.com. Information on earthquake preparedness can be found at www.daretoprepare.org.