The 15 January 2022 climactic eruption of Hunga volcano, Tonga, produced an explosion in the atmosphere of a size that has not been documented in the modern geophysical record. The event generated a broad range of atmospheric waves observed globally by various ground-based and spaceborne instrumentation networks. Most prominent is the surface-guided Lamb wave (
≲
0.01 Hz), which we observed propagating for four (+three antipodal) passages around the Earth over six days. Based on Lamb wave amplitudes, the climactic Hunga explosion was comparable in size to that of the 1883 Krakatau eruption. The Hunga eruption produced remarkable globally-detected infrasound (0.01–20 Hz), long-range (~10,000 km) audible sound, and ionospheric perturbations. Seismometers worldwide recorded pure seismic and air-to-ground coupled waves. Air-to-sea coupling likely contributed to fast-arriving tsunamis. We highlight exceptional observations of the atmospheric waves.
Seismologists have recently begun using low-cost nodal sensors in dense deployments to sample the seismic wavefield at unprecedented spatial resolution. Earthquake early warning systems and other monitoring networks (e.g., wastewater injection) would also benefit from network densification; however, current nodal sensors lack power systems or the real-time data transmission required for these applications. A candidate sensor for these networks may instead be a low-cost, all-in-one package such as the OSOP Raspberry Shake 4D (RS-4D). The RS-4D includes a vertical-component geophone, threecomponent accelerometer, digitizer, and near-real-time mini-SEED data transmission and costs only a few hundred dollars per unit. Here, we step through instrument testing of three RS-4Ds at the Albuquerque Seismological Laboratory (ASL). We find that the geophones have sensitivities constrained to within 4% of nominal, but that they have relatively high self-noise levels compared with the broadband sensors typically used in seismic networks. To demonstrate the impact this would have on characterizing nearby events, we estimate local magnitudes of earthquakes in Oklahoma using Trillium Compact broadband sensor data from U.S. Geological Survey aftershock deployments as well as 23 Raspberry Shakes operated by hobbyists and private owners within the state. We find that for M L 2.0-4.0 earthquakes at distances of 20-100 km from seismic stations, the Raspberry Shakes require events of magnitude ∼0:3 larger than the broadband sensors to reliably estimate M L at a given distance from the epicenter. We conclude that RS-4Ds are suitable for densifying backbone networks designed for studies of local and regional events.▴ Figure 1. A Raspberry Shake 4D (RS-4D) (upper-left inset) compared to the equipment used in a typical U.S. Geological Survey (USGS) aftershock deployment. Both systems incorporate a seismometer, three-component accelerometer, 24-bit digitizer, and timing information. However, the RS-4D is more than an order of magnitude less expensive.
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