Tuting-Tidding Suture Zone
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Subject: Geography
Context:
Seismicity study of Arunachal Himalaya reveals low to moderate earthquakes at two crustal depths
Concept:
- The Tuting-Tidding Suture Zone (TTSZ) is a major part of the Eastern Himalaya, where the Himalaya takes a sharp southward bend and connects with the Indo-Burma Range.
- This part of the Arunachal Himalaya has gained significant importance in recent times due to the growing need of constructing roads and hydropower projects, making the need for understanding the pattern of seismicity in this region critical.
Findings:
- Low magnitude earthquakes are concentrated at 1-15 km depth, and slightly higher greater than 4.0 magnitude earthquakes are mostly generated from 25-35 km depth.
- The intermediate-depth is devoid of seismicity and coincides with the zone of fluid/partial melts.
- The crustal thickness in this area varies from 46.7 km beneath the Brahmaputra Valley to about 55 km in the higher elevations of Arunachal, with a marginal uplift of the contact that defines the boundary between crust and the mantle technically called the Moho discontinuity.
- This, in turn, reveals the under thrusting mechanism of Indian plate in the Tuting-Tidding Suture Zone.
- Extremely high Poisson’s ratio was also obtained in the higher parts of the Lohit Valley, indicating the presence of fluid or partial melt at crustal depths.
Need for study:
- The exhumation and growth of the Himalaya is a continuous process that results predominantly from reverse faults in which the rocks on the lower surface of a fault plane move under relatively static rocks on the upper surface, a process called under thrusting of the Indian plate beneath its Eurasian counterpart.
- This process keeps modifying the drainage patterns and land forms and is the pivotal reason for causing an immense seismic hazard in the Himalayan mountain belt and adjoining regions, necessitating assessment and characterization of earthquakes in terms of cause, depth and intensity before construction activities are initiated.