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Abstract:
We used blast records from several limestone quarries in the Miami Lakes area (25.6°N, -80.3°W) northwest of Miami, Florida to estimate shallow P-wave velocities. Prior knowledge of the velocity model was lacking. We deployed a network of ten Raspberry Shake seismometers (six 3-component, four 1-component with collocated infrasound) at residential homes in the Miami Lakes region and visually identified 1639 blasts from July 2019 to February 2023. We manually picked 1450 P-phase and air-wave arrivals using the earthquake analysis software SEISAN. We know the exact locations of 350 blasts (November 2021 to June 2022) from the Miami Dade Pilot Program report and used a subset of 200 blasts with small location uncertainties in our catalog (average difference estimate-to-true: 0.9 km). The blasts occurred in three quarry areas known as White Rock Quarry (WRQ), Cemex, and Titan. We obtained average P-wave velocities from the quarries to the seismic stations of 4.36 to 4.56 km/s via linear regression. Blasts at WRQ that were nearest to the network (2 to 7 km) allow precise picking and result in a well-constrained velocity of 4.36 km/s (R-squared 0.9). Blasts at the Cemex quarries occurred between 1 to 12 km distance and we obtained a velocity of 4.56 km/s. Blasts at the Titan quarries, 8 to 15 km from the network, result in an average near-surface P-wave velocity of 4.45 km/s. The velocities are consistent with expectations for the Pleistocene Miami Limestone that is extracted, and the small variations suggest relatively homogeneous material properties.
