Sains Malaysiana 50(7)(2021): 1871-1884

http://doi.org/10.17576/jsm-2021-5007-04

 

Geophysical Characterization of a Sinkhole Region: A Study Toward Understanding Geohazards in the Karst Geosites

(Pencirian Geofizik di Kawasan Lohong: Suatu Kajian untuk Memahami Bahaya Geologi dalam Geotapak Karst)

 

SAWASDEE YORDKAYHUN*

 

Division of Physical Science, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, 90112, Thailand

 

Geophysics Research Center, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, 90112, Thailand

 

Received: 16 March 2020/Accepted: 19 November 2020

 

ABSTRACT

The outstanding geosites in Satun UNESCO Global Geopark, Thailand are mainly karst topography. Sinkhole which is originated from the dissolution of karst rocks by groundwater or acidic rainwater is one of the potential natural disasters in these geosites. To gain the confident among geotourism, detecting karst features, cavities and surficial dissolution is crucial in risk assessment and sustainable geopark management. As a part of geohazard assessment, non-invasive geophysical methods were applied for detecting near-surface defects and karst features. In this study, electrical resistivity tomography (ERT), seismic tomography and multichannel analysis of surface waves (MASW) have been integrated to understand the mechanism of an existing sinkhole formation in Satun Geopark region. ERT appeared to be an effective approach to investigate the cavity development at shallow subsurface. MASW and seismic tomography were combined to help constrain the interpretation of lithology and karst features in vicinity of the sinkhole. The results indicated that the sinkhole occurrence in this area was probably developed by forming of cavity due to an increased dissolution of the fractured limestone bedrock. This carbonate layer is in contact with the overlying groundwater and weathering shale or cohesive soil layer. The changing of water table and infiltration of surface water by heavy rainfall allowed for a sudden vertical downward of overlying sediments into the empty voids, leading to the sinkhole hazard.

 

Keywords: Geosite; resistivity; Satun Geopark; seismic; sinkhole

 

ABSTRAK

Geotapak yang luar biasa di Satun UNESCO Global Geopark, Thailand adalah topografi karst. Kawasan lohong yang berasal daripada pembubaran batu karst oleh air bawah tanah atau air hujan berasid adalah salah satu potensi bencana alam di geotapak ini. Untuk mendapatkan keyakinan di kalangan pelancongan geografi, mengesan ciri karst, rongga dan pembubaran permukaan sangat penting dalam penilaian risiko dan kelestarian pengurusan taman geologi. Sebagai sebahagian daripada penilaian bahaya geologi, kaedah geofizik tidak invasif digunakan untuk mengesan kecacatan permukaan dekat dan ciri karst. Dalam kajian ini, tomografi kerintangan elektrik (ERT), tomografi seismik dan analisis pelbagai saluran ombak permukaan (MASW) telah disatukan untuk memahami mekanisme pembentukan kawasan lohong yang ada di wilayah taman geologi Saturn. Kelihatan ERT merupakan pendekatan yang berkesan untuk mengkaji perkembangan rongga di permukaan bawah yang cetek. MASW dan tomografi seismos digabungkan untuk membantu mengekang tafsiran litologi dan ciri karst di sekitar kawasan lohong. Hasil kajian menunjukkan bahawa kejadian lubang di kawasan ini mungkin dikembangkan dengan pembentukan rongga akibat peningkatan pelarutan batuan dasar batu kapur yang patah. Lapisan karbonat ini bersentuhan dengan air bawah tanah dan lapisan serpihan cuaca atau lapisan tanah yang bersatu. Perubahan meja air dan penyusupan air permukaan oleh hujan lebat memungkinkan mendapan mendadak ke bawah ruang kosong, yang membawa kepada bahaya kawasan lohong.

 

Kata kunci: Geotapak kawasan lohong; kerintangan; seismos; taman geologi Saturn

 

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*Corresponding author; email: sawasdee.y@psu.ac.th

 

 

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