Monday, March 1, 2010

Tsunami effects in Ventura

Tsunami is a Japanese word represented by two characters: "tsu" and "nami". The character "tsu" means harbor, while the character "nami" means wave. In the past, tsunamis were often referred to as "tidal waves" by many English speaking people. Although the term "tidal wave" is a misnomer, the onshore effect is similar to the tide rapidly rising and falling.

On Saturday February 27, a massive 8.8 magnitude earthquake hit the coast of Chile. This is the same fault that produced a 9.5 quake which killed 1,655 people and left 2 million homeless in 1920. ( Saturday’s quake matched a 1906 temblor off the Ecuadorean coast as the seventh-strongest ever recorded in the world.)

A Tsunami alert was issued for the entire Pacific Ocean. Although not as catastrophic as it could have been, the effect was seen throughout the Pacific rim.

I went down to the harbor to see if the effect was visible, and when I arrived I could see a strong current that was rapidly filling the harbor. By the time I got out to the end of the south jetty, the harbor was already draining back out. I filmed the out and in flow for about an hour, and it seemed like the amplitude had dropped. Later in the day I went back down to Marina Park, and the surge was still very strong.

Reports indicated that the initial waves were the greatest, having an amplitude of plus and minus 3 feet (6 feet total!) inside the harbor. The cycle seemed to have a period of around 20 minutes, which cooincided with many of the reports around the world, including Santa Barbara and San Diego. The tide gauges show that the tsunami continued for over 48 hours.

PAGO PAGO AS 0.70M / 2.3FT 12MIN
VANUATU 0.15M / 0.5FT 22MIN
SAN DIEGO CA 0.13M / 0.4FT 20MIN

The Ventura Harbor seemed to have a physical response to this frequency. Harbors and bays are known to have a 'natural frequency,' which is a function of the length and volume of the body of water. It is possible that the Ventura Harbor was seiching, or experiencing a 'standing wave' phenomenon in response to the tsunami.

According to the Ventura County Star,

A tidal surge estimated at 3 feet rolled into Ventura Harbor about 1 p.m. and unmoored 14 residential docks in the Ventura Keys neighborhood... the Ventura Harbor Master’s Office said there was some erosion and navigational buoys came loose in the inner harbor area, but there were no major incidents. Officials said they focused on getting offshore boats into the harbor. A sailing regatta sponsored by the Pierpont Bay Yacht Club was returning to the harbor and needed assistance from the Harbor Patrol and U.S. Coast Guard to navigate the main channel.

This is video of the harbor entrance taken between 1pm and 2pm, and again after 5 pm.

Another video was posted on YouTube, and showed the effect inside the harbor at around the same time:

More information from NOAA: