Comparing land motion in Chiang Mai and Bangkok, Thailand, using Sentinel-1 InSAR Time Series

Abstract

Bangkok, Thailand's capital city, and Chiang Mai, located in northern Thailand, are both susceptible to land motion influenced by natural and anthropogenic factors. These two cities differ significantly in their geological settings and depositional environments. Bangkok's upper formation primarily consists of Neogene clay deposits, which are highly sensitive to water and prone to compaction, leading to land subsidence. Conversely, Chiang Mai's land motion is influenced by factors such as geological structure, lithology, and morphology, contributing to slope instability and subsidence. As a result, the sustainable development and preservation of these cities rely on the precise identification, monitoring, and measurement of areas prone to geological hazards.

Radar interferometry, specifically the persistent scatterer interferometry (PS-InSAR) technique, has emerged as a powerful tool for monitoring land motion due to its high resolution, accuracy, extensive coverage, and cost-effectiveness. This research employs Sentinel-1 data to effectively monitor land deformation in both Chiang Mai and Bangkok, despite their differing geological environments and depositional settings. The study combines geological, morphological, and ground measurement data to create comprehensive deformation maps.

In the analysis of land motion, 61 images from descending and ascending orbits were utilized for Bangkok, and 62 images for Chiang Mai, spanning from January 2020 to May 2023. Bangkok's land motion is primarily driven by the geological evolution of the Thon Buri Basin during the early Miocene, resulting in a deltaic plain environment dominated by Bangkok clay. Excessive construction and groundwater extraction have exacerbated land subsidence in residential areas, with an extreme subsidence rate of 24 mm/year. In contrast, Chiang Mai experiences a combination of vertical subsidence and horizontal movement influenced by factors such as depositional environment, morphology, and lithology, resulting in potential vertical motion with an extreme subsidence rate of 14 mm/year. Additionally, natural factors like precipitation and slope angles contribute to horizontal motion in the mountainous areas.

The findings highlight morphological and geological hazards affecting urban areas in Chiang Mai and Bangkok, primarily driven by natural factors including geology, morphology, and depositional environment. The PS-InSAR technique, with its high-density point measurements, effectively identifies deformation zones in both cities. Despite their distinct geological and morphological environments, both Chiang Mai and Bangkok face land subsidence issues exacerbated by rapid urbanization, leading to significant structural damage and increased flood risk in low-lying and riverfront areas. This research underscores the potential of advanced PS-InSAR techniques for geological hazard and land deformation monitoring, while also addressing the associated challenges and advantages specific to Chiang Mai and Bangkok.

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