Seismic Observations Following the July 2017 Pasco County, West Florida, Sinkhole Collapse

A sinkhole collapse on 14 July 2017 destroyed two homes and required evacuation of 9 additional residences in Land O’Lakes, Florida. The sinkhole formed rapidly and within 10 hours reached most of its final size of approximately 40 by 50 m and a maximum depth of about 15 m. According to Pasco County officials, this is the largest sinkhole to have formed in the county during the last 30 years. The site is located near two natural lakes and occurs within an area of well-developed karst. The county allowed USF geoscientists to study the sinkhole resulting in an extensive collection of LiDAR, GPR, and lake-bottom profiling data. The seismology group installed one broadband 3-component seismometer on 25 July ~20 m W of the sinkhole edge and a second one on 27 September about 10 m E of the sinkhole edge. Data are recorded continuously at 200 Hz. Drilling to understand soil structure integrity and remediation work to stabilize the sinkhole led to extreme noise levels during daytime operations through most of August 2017. Nighttime noise is lower, but due to nearby houses, sensors pick up strong 60 Hz noise caused by AC units. The only signal unequivocally attributable to the sinkhole occurred on 5 August just after stabilization work, consisting of partial backfilling with limestone rocks, began that caused the sinkhole to widen by about 3 m along its entire western edge. After completion of stabilization work, no further signals have been detected from the sinkhole. Besides sinkhole monitoring, we recorded several large global earthquakes, e.g., the Mw=8.2 and Mw=7.1 Mexico earthquakes on September 8 and 17, respectively, as well as Hurricane Irma as it passed within 20 miles as a quickly weakening category 1 hurricane. In addition to outreach and sinkhole documentation as part of a multi-sensor approach, we use the site to train seismology graduate students in field practices and conducted a class field trip.