2:45 PM - 3:00 PM
[SSS07-11] Seasonal Seismic Trends in Bangladesh: Insights from a Regional Seismic Network
Keywords:Ambient Noise Interferometry, Seismic Velocity Change, Ambient Seismic Noise Characterization, Stretching Interpolation Method, Bangladesh's Earthquakes and Microseisms, Hydrological Loading from Monsoon
Bangladesh is a tectonically active region located at the convergence of the Indian and Eurasian plates, yet its seismic network remains sparse, limiting our understanding of regional seismicity and subsurface processes. In 2016, we established the Tremble Network, a seismic array designed to enhance earthquake detection and improve ambient seismic noise analysis in Bangladesh.
Using data from the Tremble Network, we conducted a comprehensive analysis of ambient seismic noise characteristics and their implications for subsurface structure (Bin Abdul Rahman et al., 2024). Our study identified dominant noise sources, temporal variations in noise amplitude, and site effects through Horizontal-to-Vertical Spectral Ratio (HVSR) analysis. We found that microseismic noise levels fluctuate seasonally, with increased amplitudes correlating with monsoon-driven ocean activity (microseisms), while HVSR analysis revealed local site amplification effects and variations in sediment thickness across the region.
Building on this, we applied ambient noise coda wave interferometry (Hutapea et al., 2020; Nimiya et al., 2017) to examine the characteristics of cross-correlation functions (CCFs) from vertical-component ambient noise recorded between 2016 and 2020. Our analysis confirms that the CCFs exhibit coherent phase arrivals, demonstrating the stability of noise-based seismic monitoring in Bangladesh. While the investigation of temporal velocity variations is ongoing, the observed coherence suggests the potential for future monitoring of subsurface changes.
To derive virtual seismograms between station pairs, we transform seismic waveforms from the time domain to the frequency domain using the Fourier transform (Bensen et al., 2007). We then apply power-normalized cross-correlation to enhance signal coherence (Nakata et al., 2011, 2015). The stretching interpolation method (Hadziioannou et al., 2009; Minato et al., 2012) is used to estimate relative velocity changes by adjusting the time axis to maximize correlation between a reference trace (1-year stack) and a current trace (10-day stack) within a 100-second coda window.
Additionally, our preliminary earthquake catalog shows a significant decrease in earthquake occurrences during the monsoon season, similar to the findings of Bollinger et al. (2007) in Nepal. Unlike regions where rapid water infiltration increases pore pressure and promotes fault slip, Bangladesh’s thick deltaic sediments (Akhter et al., 2010) likely restrict deep fluid penetration. Instead, monsoon-induced surface loading may increase normal stress on faults, potentially suppressing earthquake activity. However, the exact mechanisms remain uncertain and require further investigation.
Recent studies (Andajani et al., 2020; Xue et al., 2021) have demonstrated how seasonal water mass redistribution influences seismic velocity variations and crustal stress modulation. Given Bangladesh’s thick deltaic sediments and monsoon-driven surface loading, understanding how these processes interact with seismic velocity and stress conditions remains an important area of investigation.
Monitoring temporal variations in seismic velocity offers valuable insights into subsurface structural changes, including stress redistribution and fluid-driven processes. Future work will focus on analyzing the relationship between seismic velocity variations, seasonal trends, and earthquake activity to better understand the underlying physical mechanisms in Bangladesh.
Using data from the Tremble Network, we conducted a comprehensive analysis of ambient seismic noise characteristics and their implications for subsurface structure (Bin Abdul Rahman et al., 2024). Our study identified dominant noise sources, temporal variations in noise amplitude, and site effects through Horizontal-to-Vertical Spectral Ratio (HVSR) analysis. We found that microseismic noise levels fluctuate seasonally, with increased amplitudes correlating with monsoon-driven ocean activity (microseisms), while HVSR analysis revealed local site amplification effects and variations in sediment thickness across the region.
Building on this, we applied ambient noise coda wave interferometry (Hutapea et al., 2020; Nimiya et al., 2017) to examine the characteristics of cross-correlation functions (CCFs) from vertical-component ambient noise recorded between 2016 and 2020. Our analysis confirms that the CCFs exhibit coherent phase arrivals, demonstrating the stability of noise-based seismic monitoring in Bangladesh. While the investigation of temporal velocity variations is ongoing, the observed coherence suggests the potential for future monitoring of subsurface changes.
To derive virtual seismograms between station pairs, we transform seismic waveforms from the time domain to the frequency domain using the Fourier transform (Bensen et al., 2007). We then apply power-normalized cross-correlation to enhance signal coherence (Nakata et al., 2011, 2015). The stretching interpolation method (Hadziioannou et al., 2009; Minato et al., 2012) is used to estimate relative velocity changes by adjusting the time axis to maximize correlation between a reference trace (1-year stack) and a current trace (10-day stack) within a 100-second coda window.
Additionally, our preliminary earthquake catalog shows a significant decrease in earthquake occurrences during the monsoon season, similar to the findings of Bollinger et al. (2007) in Nepal. Unlike regions where rapid water infiltration increases pore pressure and promotes fault slip, Bangladesh’s thick deltaic sediments (Akhter et al., 2010) likely restrict deep fluid penetration. Instead, monsoon-induced surface loading may increase normal stress on faults, potentially suppressing earthquake activity. However, the exact mechanisms remain uncertain and require further investigation.
Recent studies (Andajani et al., 2020; Xue et al., 2021) have demonstrated how seasonal water mass redistribution influences seismic velocity variations and crustal stress modulation. Given Bangladesh’s thick deltaic sediments and monsoon-driven surface loading, understanding how these processes interact with seismic velocity and stress conditions remains an important area of investigation.
Monitoring temporal variations in seismic velocity offers valuable insights into subsurface structural changes, including stress redistribution and fluid-driven processes. Future work will focus on analyzing the relationship between seismic velocity variations, seasonal trends, and earthquake activity to better understand the underlying physical mechanisms in Bangladesh.