Southern California Earthquake Hazards

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Southern California Earthquake Hazards

By Bill Normark
August 1999

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M/V Ocean Olympic

For the second year in a row, CMG's Southern California Earthquake Hazards project conducted its field activity using a leased private vessel. Such rental boats should not be confused with "ships of opportunity," which are true research vessels that are affordable and happen to be available in the right place at the right time. This year we leased the M/V Ocean Olympic, an Alaskan crab boat owned and operated by the same company that was the low-bid provider of a vessel last year. The M/V Ocean Olympic had never been used for any non-fishing activity. In the month prior to our use of the vessel, two four-person staterooms were constructed specifically to accommodate our scientific party of 12. Unfortunately, there was no time to construct an additional head (bathroom to you landlubbers).

The Marine Facilities staff turned out in force to transform this crab-fishing platform into a research vessel through the addition of four container vans that were well prepared for the task: the electronics (or underway watch) van, the MT's van, an office van, and the core-logging van (see photo on next page). The ship also had to be fitted with a winch for the Huntec DTS, a coring winch, an air compressor, a davit for the 12-kHz and 3.5-kHz towed transducers, and a small boatload of coring-related equipment for use in the sampling operation that followed the geophysical survey (see article "Sediment Sampling Off Southern California"). Using the vans and ancillary gear used in last year's operation paid dividends in that mobilization took less time by nearly a full working day.

The ship departed the CMG Marine Facility in Redwood City, California, on the morning of 4 June. It arrived about sunset the next day at the northern limit of the work area off Santa Monica, where we began work with the Huntec system. The time of day is an important aspect of describing operations during this year's survey. Because of restrictions related to concerns about marine mammals imposed by the Marine Mammal Protection Act (MMPA), the revised Coastal Zone Management Act (CZMA), and the California Coastal Commission (CCC), multichannel seismic-reflection profiling using the airgun sound source was limited to daylight hours only. At night, our surveys were restricted to use of the 12-kHz echo sounder and the high-resolution Huntec boomer system. (Note: geophysical operations offshore California are affected by four federal and state agencies; see section "Changing Climate for Offshore Surveys"). The underlying regulations are based on federal law and are expected to be enforced in all U.S. coastal waters eventually.

Deck vans (view aft) with office van in foreground, mechanical shop behind to left, electronics van behind to right, and core van farthest aft.

The daily operational scheme throughout the survey was to conduct multichannel seismic work between about 0530 and 2020 each day and then break off the survey line to conduct Huntec "site" surveys. In the morning, we would rejoin the multichannel transects. The scientific party assembled for standing watch during geophysical work consisted of Ray Sliter, Jane Reid, and Dave Holton. Three contract biologists from the Cascadia Research Collective were also aboard to provide mammal observations to help us stay in compliance with the directives of the CCC and the IHA (Incidental Harassment Authorization, a permit granted by the National Marine Fisheries Service). Compliance meant that we shut off the airgun whenever marine mammals came within designated ranges of the sound sources. Typically, this resulted in two to four shutdowns each day lasting from 2 to 10 minutes each. Last year, two mammal observers provided 24-hour surveillance, but the additional restrictions this year resulted in a requirement to have two biologists on watch at all times during daylight hours.

There were no major equipment failures during the entire 12-day survey, thanks in large measure to the efforts of Larry Kooker, Kevin O'Toole, Fred Payne, Hal Williams (all of our Marine Facility group), and Graham Standan of Geoforce, Inc. As a result, we were able to collect about 1,250 km of high-resolution multichannel seismic data. An additional 1,050 km of Huntec-only data were obtained during the night operations. On the last day of the cruise (17 June), Jon Childs and Pat Hart met us with a small dive boat to conduct acoustic source-level measurements of the Huntec and GI gun systems. We also tested the sparker sound source in the Huntec for evaluation by Brian Edwards for his proposed work next year on the shelf off Long Beach. Paralleling last year's operation, the Ocean Olympic was used for back-to-back cruises to save money by sharing mobilization/demobilization costs. Brian Edwards and Homa Lee took command in San Diego to continue their coring program off Santa Monica, in addition to obtaining piston cores for benefit of the earthquake hazards project (See article "Sediment Sampling in Southern California").

Changing Climate for Offshore Surveys (Or No Airgun Sound Source is Small Enough)

Deploying small GI gun in pre-dawn twilight to be ready to commence multichannel seismic data collection when visibility is sufficient for marine-mammal observers.

During last year's survey using multichannel seismic-reflection and Huntec systems offshore southern California, the project contracted with Cascadia Research Collective to provide two personnel for continuous (24 hour/day) observation and recording of marine-mammal sightings. The USGS also voluntarily adhered to operational restrictions in the Marine Mammal Protection Act (MMPA). This meant that the multichannel sound sources used (40 cu in. airgun or 35 cu in. GI gun at different times during the cruise) would be shut down whenever marine mammals came to within specified distances. The protocols for shutdown of the sound sources were established prior to sailing, and the decision to shut down was vested solely with the marine-mammal observers and was not subject to veto by the chief scientist. Shutdown was required when baleen whales approached within 200 m of the sound source and when odontocetes (e.g., dolphins) or pinnipeds (e.g., seals) came within 100 m. The protocol area was not a simple radius from the sound sources but an egg-shaped area that extended forward of and along the sides of the vessel by the stated protocol range. Sea lions, dolphins, and whales were observed numerous times during the survey, requiring shutdowns as frequently as several times a day. Most shutdowns were on the order of 2 to 8 minutes in length and tended to occur in the same general areas on each transit (e.g., where dolphins were feeding in waters above the upper slope), so it was not practical to retrace any trackline to acquire missing data. The report of the marine-mammal observers is included as an appendix to the Normark et al. (1999) cruise report.

For this year's field operation, the National Marine Fisheries Service (NMFS), the agency empowered to enforce the MMPA, required that the USGS apply for an Incidental Harassment Authorization (IHA). The IHA request process nominally takes 120 days and the request was submitted to NMFS in mid-January 1999. One part of the IHA process requires NMFS to make the application available for public comment, which is done through notification in the Federal Register.

Following publication of the IHA request in the Federal Register, the California Coastal Commission (CCC) used authorization granted by provisions of the revised Coastal Zone Management Act to require the USGS to submit a Consistency Determination (CD). The CD documents that a federal activity (in this case the geophysical survey) will be conducted in a manner consistent with the State's coastal-zone management program. The process of application to the CCC included discussion and review at a monthly meeting of the CCC; for this cruise activity, the hearing was in May. The original request for a CD was denied, and the CCC requested that the USGS resubmit with additional conditions, this time requesting a Negative Determination (i.e., a finding that the proposed activity would have no effect on coastal-zone resources). The USGS complied and received verbal approval prior to the cruise. The most significant condition required by the CCC action was that airgun operations not be conducted during darkness.

After responding to questions raised as a result of the public comment period (including follow-up discussions between the USGS and NMFS), the USGS received the IHA on 3 June 1999. The IHA incorporated the conditions from the CCC and specified, among other restrictions, that

the USGS would have a minimum of three properly trained mammal observers approved in advance by NMFS;

the observers would record the effects of Òseismic surveys and the resulting noise on marine mammalsÓ and that monitoring would occur at all times the system was operating;

the protocol for shutdown of the sound source would be 100 m for dolphins, seals, and sea lions, and 250 m for whales;

the USGS would "not conduct seismic surveys with the GI-gun sound source at night when visibility limits marine mammal detection within the designated safety zone"; and

the results of the monitoring will be reported to NMFS within 120 days from the end of the geophysical survey.

At the beginning of the field program, the marine-mammal observers provided a written protocol for the geophysical watchstanders with respect to meeting the conditions of the IHA. This marine-mammal protocol was stated:

In the morning: Watchstander in the electronics lab will "contact . . . . mammal team to check if [the] area is clear of animals before" commencing use with the GI gun.

In the evening: The "mammal team" will contact the watchstanders in the electronic van "when light conditions are too poor to detect animals within the shutdown zone."

Shutdowns—"when called for . . . .will be radioed in a single transmission, i.e., 'E-van --- Mammal Team --- shut down.'"

All communication between the mammal team and the geophysical watchstanders was by radio using the same channel that was used for communication with the ship's bridge watch. Thus, all personnel on watch were aware of any communications affecting either the vessel or scientific operations regardless of which work area was initiating the transmission.

The written protocol also stated the "cut-off distances": "100 m [for] dolphins, seals, and sea lions" and "250 m [for] large whales." The observers also requested that "if animals are seen off the stern, clearly within [the] shut down area and haven't been detected by [the] mammal team" . . . . then the watchstanders were to shut down the GI gun and immediately contact the mammal team.

All conditions stated in the protocol were followed throughout the cruise.

The program cost for meeting the requirements of the IHA are twofold. First, the number of pay periods of CMG personnel involved in the permitting process, which lasted from mid-December to early June, is equal to the number of pay periods for the 8-member CMG scientific staff during the 12 days of survey. Second, loss of multichannel seismic-reflection data collection during the night amounts to 38% of the total ship days contracted; for this year's 12-day survey, this amounts to more than $30K.

Another restriction on the survey resulted from the authority of the California State Lands Commission (SLC). The SLC has regulatory authority over waters within 3 miles of the coast. At present, the SLC bans all airgun seismic sound sources regardless of size and regardless of the intended use. For example, scientific research to define earthquake hazards cannot obtain an exemption to the ban. As a result, the survey with the GI gun could not extend within 3 miles of the coast. The SLC does not have restrictions on non-airgun sources such as the Huntec boomer system, but the geophysical survey lines were terminated at the 3-mile limit because Huntec boomer data by itself are insufficient for mapping fault systems in this area.

The important point of the above discussion is that these restrictions represent a problem not just for those who want to work offshore California. All of the coastal states will be developing, or have in place, management plans of their own under the revised CZMA, and the provisions of the MMPA apply everywhere with respect to U.S. oceanographic research. At present, not all areas of the oceans have come under strict enforcement, but it may only be a matter of time. "Establishing a precedent" was a key issue for the agencies acting on the approval process for our recent survey.

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August 1999

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in this issue: Southern California Sediment Sampling

Earthquake Hazards

Chesapeake Bay

Georges Bank

Glacier Bay National Park

Plume Study

Los Angeles

USGS / University Collaboration

Scientist in the News

Trouble in Paradise

Oceanographic Processes

Florida Keys Geology

Dry Tortugas Nat'l Park

Sustainable Seas

Ecosystem Workshop

Coastal Sediments '99

Association for Women Geoscientists

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