Seismic Observations of Precipitation and Recharge-Related Signals in the Floridan Aquifer at Santa Fe River Sink and Rise, Florida

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Environmental seismology encompasses a broad range of Earth surface processes. Such studies have primarily focused on hillslopes to obtain information on landslides, on glaciers to investigate ice movement and subglacial water flow, and on rivers to characterize turbulent flow, discharge, bedload, and sediment transport. However, environmental seismology has not been fully utilized to investigate the unique subsurface processes which occur within a karst aquifer. Monitoring karst systems is of growing concern due to the significant percentage of people who rely on them as a source of fresh water as well as for hazard assessment related to sinkhole formation. In May 2018, we deployed two co-located geophysical arrays to observe recharge-induced responses of subsurface water flow in a karstic conduit network known as the Santa Fe River Sink-Rise system in north-central Florida, which is where the Santa Fe River (average 31 m³/s) is captured by a sinkhole and flows ~6 km through a network of water-filled caves to River Rise, a first magnitude spring. The first of these arrays is a seismic network consisting of 12 L-22 and two broadband (CMG 3T) seismometers, and the second consists of two platform and four borehole tiltmeters. We also deployed 19 hydrologic sensors (4 level and temperature, 14 level, temperature, and conductivity, and 1 barologger) in 11 wells, five karst windows, and at River Sink and River Rise, and are collecting meteorological data onsite. Based on preliminary review of the seismic data, we find increases in seismic amplitudes and power in frequency bands of 1-150 Hz during and subsequent to significant precipitation events of at least 10 mm over a half-hour span. Given the presence of a signal after precipitation ceases, additional processes beyond simply the precipitation must contribute to the seismic signals, for instance discharge related pressure pulses. Further examination of the seismic data, reinforced through modeling, tilt, hydrologic, and meteorological data, should elucidate the specific processes generating the observed signals.

Presenting Author: Jacob A. Gochenour

Authors