Major Earthquake Strikes Bhutan in 1714
On 4 May 1714, Bhutan experienced a catastrophic earthquake estimated at a magnitude of about 8.1 Mw. The seismic event resulted in violent shaking reaching a level IX on the Modified Mercalli Intensity scale. It is believed that this earthquake was caused by the rupture of the Bhutan section of the Main Frontal Thrust, leading to widespread destruction in west central Bhutan and northeastern India, resulting in “many fatalities.”
Tectonic Setting
Bhutan is situated at the southern margin of the Himalayas, a mountain range formed by the ongoing collision of the Indian Plate with the Eurasian Plate. Major thrust faults characterize this active tectonic region, with the primary structure being the Main Himalayan Thrust (MHT). This thrust links directly into the plate boundary to the north and serves as the décollement for the entire thrust system. The southernmost thrust that surfaces in this region is known as the Main Frontal Thrust (MFT), which connects with the MHT at depth. Other significant thrusts, such as the Main Central Thrust and the Main Boundary Thrust, branch off the MHT and are all capable of causing devastating earthquakes.
The Earthquake Event
Historically, this seismic event was originally recorded as occurring in 1713; however, further investigations have pinpointed the year to 1714. This conclusion is supported by records from northeastern India, which indicate that the earthquake occurred shortly before the passing of King Rudra Singh in August 1714.
The earthquake’s magnitude and specific location have been estimated based on seismic intensity data collected from damage reports in both Bhutan and India. Paleoseismological studies, including trench investigations across the Main Frontal Thrust, have provided additional insights. Evidence of surface rupture linked to this earthquake has been discovered at three key sites along the MFT in Bhutan, with the largest displacement noted to be approximately 11 m, near Samdrup Jongkhar close to the Bhutan-India border. The estimated rupture length along the mountain front ranges from a minimum of 175 km to potentially 290 km.
On the same day of the earthquake, reports indicated that around thirty aftershocks occurred, with additional aftershocks continuing throughout the month.
Damage and Impact
The devastating effects of the earthquake were documented by Shakya Rinchen, the Chief Abbot, who experienced the tremors at the age of four. Descriptions of the intensity of the quake were provided for three significant locations: Wangdue Phodrang, the Punakha valley, and the Thimphu valley. Furthermore, the Gangteng Monastery in Phobjikha Valley suffered significant damage. Reports also indicate destruction in northeastern India at locations such as Tingkhong, Charaideo, and Garhgaon. The only available record concerning casualties is the vague mention of “many fatalities.”