ABSTRACT
Seismographs record earthquakes and also record various types of noise, including anthropogenic noise. In the present study, we analyse the influence of the lockdown due to COVID-19 on the ground motion at CSIR-NGRI HYB Seismological Observatory, Hyderabad. We analyse the noise recorded a week before and after the implementation of lockdown by estimating the probability density function of seismic power spectral density and by constructing the daily spectrograms. We find that at low frequency (<1 Hz), where the noise is typically dominated by naturally occurring microseismic noise, a reduction of ~2 dB for secondary microseisms (7–3 s) and at higher frequency (1–10 Hz) a reduction of ~6 dB was observed during the lockdown period. The reduction in higher frequencies corresponding to anthropogenic noise sources led to improving the SNR (signal-to-noise ratio) by a factor of 2 which is the frequency bandwidth of the microearthquakes leading to the identification of microearthquakes with Ml around 3 from epicentral distances of 180 km.
ABSTRACT
Yangon has a population of over seven million and is one of the fastest growing cities in Myanmar. Like many of Myanmar's large cities, it is located in close proximity to the Sagaing fault, a major strike-slip fault in Southeast Asia that has historically produced magnitude >7 earthquakes. In addition, the Indo-Myanmar region hosts complex tectonics related to the subduction of the India plate beneath the Burma microplate and large magnitude earthquakes are expected for the locked part of the subduction system. An improved assessment of the ground motions that may occur during a large earthquake rupture can lead to better city planning and management to help prevent the loss of life and property in Myanmar's expanding population centers. This requires an improved understanding of the subsurface and geologic structures that underlie the major cities. As part of the Myanmar Universities Seismic Experiment (MUSE) project, 11 professors and students in Yangon were remotely trained during the COVID-19 lockdown on the installation of nodal seismic stations. We have recorded data at 110 three-component nodes from the IRIS PASSCAL instrument center. Instruments were deployed along three densely spaced seismic profiles in one of the first US-based international efforts of this kind. Data recording started on 21 March 2020 and continued for ~30 days. Following a similar study in Los Angeles, California, we will use receiver function computed from recordings of eight teleseismic earthquakes to determine the depth to basement beneath Yangon. These results and other seismological analyses will aid in providing better estimates of ground shaking in the event of moderate-large earthquakes. © 2021 Society of Exploration Geophysicists First International Meeting for Applied Geoscience & Energy
ABSTRACT
The Samos Island (Aegean Sea) Earthquake occurred on 30 October 2020. It produced a tsunami that impacted coastal communities, ground shaking that was locally amplified in some areas and that led to collapse of structures with 118 fatalities in both Greece and Turkey, and wide-ranging geotechnical effects including rockfalls, landsliding, and liquefaction. As a result of the global COVID-19 pandemic, the reconnaissance of this event did not involve the deployment of international teams, as would be typical for an event of this size. Instead, following initial deployments of separate Greek and Turkish teams, the reconnaissance and documentation efforts were managed in a coordinated manner with the assistance of international partners. This coordination ultimately produced a multi-agency joint report published on the 2-month anniversary of the earthquake, and this special issue. This paper provides an overview of the reconnaissance activities undertaken to document the effects of this important event and summarizes key lessons spanning topic areas from seismology to emergency response.