Passive acoustic monitoring complements traditional methods for assessing marine habitat enhancement outcomes

Habitat enhancement, often accomplished through the introduction of artificial structures, is a common strategy used by marine resource managers to provide habitat subsidies, protect sensitive habitat, and create new fishing opportunities. Traditional monitoring methods for assessing habitat enhancement outcomes face numerous limitations, including dependence on environmental conditions and trade-offs between sampling frequency and duration. Passive acoustic monitoring (PAM) is not subject to these same limitations and offers many advantages as a complement to traditional monitoring methods. Our team opportunistically monitored the soundscape and community development of a newly deployed artificial reef and compared it to that of a nearby established artificial reef using PAM and underwater time-lapse videos. Specifically, we compared the sound pressure level (SPL) timeseries, dusk peak in SPL, and dusk power spectrum between the two artificial reefs to evaluate whether and on what timescale the soundscapes converged. Additionally, we tracked temporal patterns in species-specific vocalizations to identify the trajectory of community development on the new reef. Lastly, we compared the qualitative conclusions drawn from PAM to previously published results from video monitoring of the same two artificial reefs. PAM identified minimal difference in mean low-frequency SPL between the two reefs at the onset of monitoring. Though the timeseries correlation, dusk SPL, and dusk power spectra all varied across sampling periods, there were periods of low-frequency soundscape alignment at four and eleven months following artificial reef deployment, associated with the presence of fish chorusing. The high-frequency timeseries on each reef were well correlated during all sampling periods, despite an initial SPL difference of 17 dB. Throughout monitoring, high-frequency sound levels became more similar between the reefs but did not converge. While video monitoring suggested that demersal species did not colonize the reef until five months post-deployment, patterns in species-specific vocalizations suggested that toadfish (Opsanus sp.) a cryptic, demersal species may have colonized the new reef within two weeks. Our findings demonstrate that passive acoustic monitoring is a useful complement to traditional methodologies and can provide a more holistic view of community development than visual monitoring alone

The Mw 5.1, 9 August 2020, Sparta Earthquake, North Carolina: The First Documented Seismic Surface Rupture in the Eastern United States

At 8:07 a.m. EDT on 9 Aug. 2020 a Mw 5.1 earthquake located ~3 km south of Sparta, North Carolina, USA, shook much of the eastern United States, producing the first documented surface rupture due to faulting east of the New Madrid seismic zone. The co-seismic surface rupture was identified along a 2-km-long traceable zone of predominantly reverse displacement, with folding and flexure generating a scarp averaging 8–10-cm-high with a maximum observed height of ~25 cm. Widespread deformation south of the main surface rupture includes cm-dm–long and mm-cm–wide fissures. Two trenches excavated across the surface rupture reveal that this earthquake propagated to the surface along a preexisting structure in the shallow bedrock, which had not been previously identified as an active fault. Surface ruptures by faulting are rarely reported for M <6 earthquakes, and hence the Sparta earthquake provides an opportunity to improve seismic hazard knowledge associated with these moderate events. Furthermore, this earthquake occurred in a very low strain rate intraplate setting, where earthquake surface deformation, regardless of magnitude, is sparse in time and rare to observe and characterize

Seismic character of volcanic activity at the ultraslow-spreading Gakkel Ridge

Never before has a volcanic eruption on a slow- or ultraslow-spreading mid-ocean ridge been both observed seismically and confirmed on the seafloor. During the first half of 1999, a long-lived volcanic-spreading event occurred on the ultraslow-spreading Gakkel Ridge in the Arctic Ocean. The seismicity associated with this event was unprecedented in duration and magnitude for a seafloor eruption. Sonar images from the U.S.S. Hawkbill, which passed over the area within four months of the start of activity, are consistent with the presence of a large, recently erupted flow and a volcanic peak directly in the area of seismic activity. Seismic activity began in mid-January and continued vigorously for three months; a reduced rate of activity persisted for an additional four months or more. In total, 252 events were large enough to be recorded on global seismic networks. Although a limited number of volcanic-spreading events have been observed globally, the duration and magnitude of the Gakkel Ridge swarm, when compared with volcanic seismicity at ridges spreading at intermediate and fast spreading rates, suggest that a negative power-law relationship may exist between these parameters and spreading rate. Fault activation, in response to magmatic emplacement, appears to have occurred over a broad region, suggesting that magma may have been tapped from mantle depths. The slow migration of the largest magnitude events along the axis of the rift valley suggests multiple magmatic pulses at depth. In combination with bathymetric setting and sidescan sonar confirmation, the seismic data for this event have provided a unique look at the scale and character of eruption processes at ultraslow-spreading rates.Academi