Historically, concern for tsunamis along the California coast has been limited to distant sources such as Alaska, Chile, or others. A detailed assessment of remotely generated tsunami impacts prepared by the U.S. Army Corps of Engineers in 1980 has been used for design guidelines to the present time. However, a few studies have been published recently suggesting potential tsunami sources within the Southern California Bight which could have a greater impact to the Ports due to the short travel distance and higher wave amplitudes than expected from the remote sources.

The potential sources for locally generated tsunamis evaluated for the Ports are based on previous investigations conducted at the University of Southern California. These preceding analyses are based on the concept that large destructive tsunamis can be generated by local faults, which are primarily strike-slip faults in the Southern California Continental Borderland (SCCB). Considering strike-slip faults as potential tsunami sources is relatively new since tsunamis throughout the world typically have been generated only by mega-thrust faults along oceanic subduction zones where great, global scale plates converge (e.g. 2004 Sumatra, 1964 Alaska, 1960 Chile). In addition to such megathrusts, local tsunamis have been generated by landslides and volcanic events and consequently the study also considers local potential landslides.

The tsunami sources of concern, illustrated in the figure below, involved the following four faulting scenarios:

• Santa Catalina fault (CAT), all seven segments,
• Santa Catalina fault, segments 5, 6, and 7,
• Three segments of the Lasuen Knoll fault (LAS), and
• San Mateo thrust (SAM).

The tsunamis from these sources are assumed to be generated by Mw =7.0 to 7.6 earthquakes. The analysis also includes two landslide scenarios predicated on landslides occurring at two locations along the Palos Verdes Escarpment (PVS1 and PVS2 in the figure); one where a previous landslide occurred about 7,500 years ago, and the other along the same escarpment where there has not yet been a slide.

Location of Potential Local Tsunami Sources
The seismicity and tectonics of the Southern California Continental Borderland (SCCB) were analyzed to help characterize the potential for tsunami-generating earthquakes. The analysis indicated the SCCB has few restraining bends with thrust-type faulting sources large enough to generate significant tsunamis, and therefore tsunamis appear to be extremely infrequent. Large earthquakes (M~7.5) required for tsunami generation are very infrequent and have not occurred in the offshore area of California within historical times. Furthermore, not every large earthquake is expected to generate a tsunami based on historical occurrences of tsunamis and seismic activity throughout the world. Based on the seismicity, geodetics, and geology, a large locally generated tsunami from either local seismic activity or a local submarine landslide would probably not occur more than once every 10,000 years and this estimate is believed to be conservative.

Despite the low risk of local tsunami generation, the tsunami impacts investigation also included a detailed computer simulation of the wave propagation from the representative four seismic sources and two Palos Verdes Landslide sources. From the model results for the six scenarios simulated, the worst case scenario for the Port of Los Angeles is for the Palos Verdes II submerged landslide scenario.

The tsunami propagation results from an approximately two hour simulation of the Palos Verdes II submerged landslide scenario are illustrated in the following figure where the maximum water levels relative to mean sea level during the simulation are illustrated. The results indicate higher maximum water levels in areas of wave focusing and wave reflection such as the eastern side of Pier 400 and the outer harbor area of the Port of Los Angeles. For the Palos Verdes submerged landslide scenario, water levels exceed adjacent typical deck elevations of approximately 3.7 m above mean sea level in some localized areas. Maximum water levels exceed 7 m along limited areas of the west and southwest faces of Pier 400 in the Port of Los Angeles and are as high as 6.5 m along the Navy Mole in the Port of Long Beach. There are also higher water levels in the open water area west of Pier 400 resulting from wave reflection from the adjacent pier landfills. The results from all of the other scenarios simulated indicated lower maximum water levels when compared to this scenario.

Maximum Water Levels for Palos Verdes II Landslide Scenario
The water level time histories for several locations within the Port of Los Angeles are illustrated in the figure below for the Palos Verdes II submerged landslide scenario. The typical deck elevation is also illustrated in this figure to provide some information about expected overtopping. The results support the conclusion that the majority of the locations will not experience overtopping and for those locations that do experience overtopping, the duration is sufficiently short that the volume of water, and therefore the inundation area, is not expected to be great.

Water Level Time History for Palos Verdes II Landslide Scenario
The principal characteristics of the tsunamis in the Ports are given in the following table where the travel times and characteristic wave periods are given. For the four local seismic tsunami sources, the travel time to the Ports ranges from 21 to 29 minutes. For the two local landslide tsunami sources, the travel time is just a little over 10 minutes after the earthquake.