Instrumentation and Quantification of Tsunamis With an Emphasis on the Santa Barbara Channel

Quantifying Earthquake & Tsunami Strength Seismographs & seismometers—calculate magnitude, and epicenter Tide Gauges Run-up measurements Satellite Altimetry Numerical Model Simulations ADVs, ADCPs, pressure gauges, etc on ocean floor

Proxies for Tsunami strength Wave amplitude (Height) Wave speed Vertical/horizontal displacement by crustal plates Seismic energy, wave energy and propagation

Seismology Data Broadband Seismometers (top right) measure different frequency motion Identify long-period events from far away, and local events Detect all motions, including local landslides and distant earthquakes Seismograph measure P and S waves. Difference in arrival time used to calcuate epicenter of earthquake Use these data to issue Tsunami Warnings; takes ~5min Data are also input into models for simulation of potential Tsunami

Tidal Gauges Tide gauges (top) and Buoys (bottom) often provide first confirmation of tsunami generation. Buoys with bottom pressure sensors contribute real- time data to Tsunami warning system Tide gauges measure changes in pressure relative to mean trends and bottom depth Problems: not all tide gauges sample at same frequency—ever 2 min, 6 min, 30 min, etc. varies by location

Schematic of Tide Gauge (left) and deployed Tide Gauge (right)

Tide gauge results from Sumatra Tsunami 2004

Deep-ocean Assessment and Reporting of Tsunamis (DART) ~39 Surface buoys with bottom pressure sensors Conversion factor ~10dbar = 10 meters DARTS also incorporates data ~400 tide gauges worldwide. DARTS transmit data every 15 min; during Tsunami warning data is time averaged every minute and transmitted every 8 minutes

Terrestrial run-up and inundation by tsunamis Tsunamis behave like shallow- water waves because of long wavelength; used to forecast inundation and amplitude of waves by modelers By knowing ocean bathymetry, wave speed can be predicted, giving estimate of arrival time on land

Short-term Inundation Forecast for Tsunamis (SIFT) Developed by NOAA Pacific Marine Environmental Laboratory, or PMEL, to predict tsunami propagation Model uses seismological data and DARTS data to predict impact on different coastal locations

MOST (method of splitting tsunami) model

Numerical model that uses forecast techniques and real-time data Incorporates satellite altimetry data, tide gauge data, and seismographic data seafloor displacement, horizontal extent of displacement, and its location are most important for determining propagation

Offshore Southern California Tsunamigenic Hazards Several active submarine thrust fault systems The walls of the basin forming the channel are susceptible to submarine slope failures

Fault Lines in the Santa Barbara Region

Historical Tsunamis and Earthquakes Offshore Southern California December 21, 1812 Affected over 60km of the coast ~7.2 magnitude – one of the largest in California history Runup: 4m at El Refugio, ~2m in SB and Ventura, possibly a 4m in Kona, Hawaii “the sea receded and rose like a high mountain” Residents relocated their settlements further inland after the tsunami

Historical Tsunamis and Earthquakes Offshore Southern California November 4, 1927 – Point Arguello-Lompoc Largest and best observed locally generated tsunami Magnitude ~7.0 Offshore thrust or oblique-reverse fault west of Pt. Conception Runup: 2m at Surf Exceptionally high tide elsewhere

Santa Barbara Basin & the Goleta slide Submerged extension of the Ventura Basin Goleta slide: 9 miles x 6.5 miles Steep slide from 300 ft to >1800 ft Slopes as steep as 45 deg 8-10 kilo annum years ago Cause of concern because of oil drilling!

Santa Barbara Basin

Triggers Landslide Major earthquakes are the most obvious landslide triggers Subsurface fluid flow The rate of sediment accumulation in the shelf-edge delta Destabilizing influence of structural growth 30-40% probability of landslide in next 60,000 years Landslide to Tsunami Water depth: too deep, and landslide would propagate southward waves Landslide volume: all or part of the remaining volume of the Goleta slide could potentially fail Landslide speed: m/s are required to trigger a tsunami Potential runup: 2-20m of 10km shoreline Good news: Goleta slide is relatively stable!

Landslides are South-facing