Mud Creek Landslide, Big Sur California
Before and after images of the Mud Creek landslide located in Big Sur California. The landslide occurred in the late spring of 2017 following an above-average amount of precipitation in central and northern California. Ground-base InSAR monitoring began about 1-month after the failure. The radar was located on a constructed pad on the toe of the landslide just above the ocean. By October 2017, the relentless onslaught of ocean eroded much of the fluffed up toe debris resulting in the removal of the radar unit.
Mud Creek Landslide, Radar Displacement Map
The screenshot image above shows radar data (colored) overlaid on a DTM. The yellow rectangle box is the location of the radar unit sitting on the toe of the slide close to the Pacific Ocean. The failure date was May 20, 2017, and the data above shows displacement for 5-days in July. The radar software allows the user to view the most current data or quickly adjust to any interval of time during the project. The five-day displacement interval exhibits at least 30 inches of movement shown as small black areas on the head scarp area. The spotty high rates of displacement occurring on the slope months after the main failure initiated much rockfall that created a dangerous environment during work to reopen Highway 1. A successful rockfall warning method, using radar velocity data, was developed specifically for this site and is described in detail on a blog post on this site.
Mud Creek Landslide, 24-Hour Displacement Map
About 1-month after the failure high rates of displacement are still affecting the site. Area 13 is exhibiting locations of at least 25-inches of displacement during a 24-hour interval. The displacement interval above exhibits data about an hour before failure and several hours after the failure. Reviewing data from additional time intervals suggest that several smaller raveling events occurred after the primary failure event at 1:27 AM.
Area 13, Cumulative Displacement Time Series
Cumulative displacement time series data can be observed at any time interval at any time during a project. However, as a project increases with time it is crucial that the monitoring professional review time series data at different time intervals. Longer intervals provide a view of overall movement trends but small acceleration events and failures can get lost in the larger scale of data as shown in this screenshot above. Using, alarm settings, observations of displacement, velocity, and inverse velocity needs to be actively reviewed at least daily but preferably several times a day.
Area 13, Inverse Velocity Time Series
Several important observations can be made from the inverse velocity data exhibited above. From left to right the low inverse values of about 10 and the horizontal data trend indicate a high rate of steady displacement is occurring. On June 29 at 4:38 AM a progressive or acceleration trend began and after several hours the approach to data linearity became distinct. After the failure, a regressive trend ensued with decreasing rates exhibited by the upward trend correlated by increasing inverse velocity values and the increase of data fluctuations as the regression trend continues moving to the right side of the data.