A tsunami is a series of powerful ocean waves generated by the sudden displacement of a large volume of water, typically from an undersea earthquake. While the San Diego coastline is often perceived as having a lower risk compared to the Pacific Northwest, it remains exposed to Pacific-wide seismic activity. The region’s geographical position has historically shielded it from catastrophic waves, yet the potential for damaging events still exists. This article clarifies the historical record of tsunamis in San Diego and outlines the primary risks and current safety measures in place for the region.
Addressing the Historical Record
San Diego has not experienced a destructive, locally generated tsunami in its recorded history. The most significant historical wave events have been from distant sources, known as teletsunamis.
The largest recorded wave run-up resulted from the 1960 Great Chilean Earthquake, a magnitude 9.5 event that produced a maximum wave range of approximately 1.5 meters (4.9 feet) in San Diego Bay. This event caused strong currents that damaged piers and temporarily halted ferry service but did not result in widespread inundation. The 1964 Great Alaska Earthquake and the 2011 Tohoku, Japan, earthquake also generated significant distant-source tsunamis, causing noticeable surges and damaging currents within the harbor. The only documented local event was a small disturbance following a local earthquake in 1862.
Primary Sources of Tsunami Risk
Despite the quiet historical record, the San Diego coastline is vulnerable to two primary mechanisms for tsunami generation: far-field and local sources. Far-field tsunamis are generated by major earthquakes in distant areas like the Aleutian Islands, Alaska, Japan, or the west coast of South America. These waves travel across the entire Pacific, giving authorities many hours to issue warnings before they arrive.
The most concerning local risk comes not from large offshore fault movements but from submarine landslides. The continental shelf offshore of San Diego is steep and contains large sediment deposits that could slump following a strong earthquake, such as one on the nearby Coronado Bank Fault. This type of local event would generate a rapid-onset tsunami, potentially arriving on the coast in minutes, leaving very little time for official warnings. Modeling suggests that while San Diego Bay is partially protected by Point Loma, these local sources could still produce the highest waves and most dangerous currents within the harbor.
Current Warning and Response Systems
The institutional response to a potential tsunami threat begins with the National Tsunami Warning Center (NTWC), which is part of the National Oceanic and Atmospheric Administration (NOAA). The NTWC uses a network of seismic sensors and Deep-ocean Assessment and Reporting of Tsunami (DART) buoys to detect and forecast wave movement across the Pacific. Once a threat is confirmed, the information is relayed to the California Governor’s Office of Emergency Services (Cal OES) and then to the San Diego County Office of Emergency Services.
San Diego County utilizes the AlertSanDiego system to coordinate warnings to the public. This system functions as a reverse-911 for landlines and sends alerts to registered cell phones, Voice Over IP phones, and email addresses. Additionally, the federal Wireless Emergency Alert (WEA) system broadcasts short, location-specific warnings to all compatible cell phones, providing an immediate notification channel for residents and visitors.
Personal Safety Measures
Residents and visitors must understand the differences between the official alert levels to ensure an appropriate response.
A Tsunami Watch means a distant earthquake has occurred and a tsunami is possible; the public should remain alert and await further information. A Tsunami Advisory indicates that strong currents or waves dangerous to those in or near the water are expected, and people should stay out of the ocean, harbors, and waterways. The most urgent alert is a Tsunami Warning, which signifies that a tsunami with widespread inundation potential is imminent or occurring, requiring immediate evacuation.
Beyond official alerts, the public must recognize natural warning signs, such as a strong earthquake lasting 20 seconds or more, or a sudden, unusual recession of the ocean water. Upon seeing any of these signs, people should immediately move inland or seek high ground, aiming for an elevation of at least 100 feet above sea level or moving two miles inland.