Invited Talk
Exploring the Deep Structure Beneath Indo-Burma Orogenic Belt and its Geodynamic Implications
Yang SHUN, Zhejiang Ocean University
yangshun@zjou.edu.cn

Biography

Dr. Shun Yang is a young assistant professor at the Marine Science and Technology College, Zhejiang Ocean University. He received his Ph.D. in Solid geophysics from the Institute of Geology and Geophysics, Chinese Academy of Sciences in 2023.

Dr. Shun Yang’s research interests include crust-mantle structure imaging and seismicity analysis. His research has made contributions to advancing the understanding of convergent mode between Indian-Asian continents, as well as seismicity features in Myanmar.

Indo-Burma orogenic belt occupies the southern end of the eastern Himalayan syntaxis (EHS). It has the common tectonic characteristics of the EHS, such as oblique collision and subduction, and is less affected by severe shortening and rotational deformation. Thus, it is an ideal place to probe the subducted relics of the Neo-Tethyan ocean and the morphology of modern subducted slab, and related deep dynamic process. Additionally, controlled by oblique subduction of the Indian plate, Myanmar is also a seismically active region. The study of seismicity in Myanmar can help understand the shallow tectonic response of oblique subduction and potentially mitigate the seismic hazard and risk. Based on the seismic data recorded at the recently deployed China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO I and II) seismic network in south-central Myanmar, this study constructs the structure of the subduction system beneath the Indo-Burma orogenic belt, and it reveals the geometry and stress state of the active crustal faults.

The upper mantle imaging from finite-frequency teleseismic P-wave tomography in south-central Myanmar reveals three N-S-trending, slab-like seismic high-velocity anomalies. The opposite dipping anomalies (HV1 and HV2) beneath the Indo-Burma Range exhibit various geometric characteristics along the strike. The HV1 exhibits an eastward dipping, with its along‐dip length decreasing from ~700 km at 24°N to ~400 km at ~21°N. It has velocity perturbations of 2.0 to 4.0% and a thickness of ~100 km. The HV2 along‐dip extent is the shortest (~200 km) and most gently westward dipping (~12°) in the north (~23.5°N). The dipping angle and along-dip length of HV2 increase progressively southward, reaching ~60° and ~450 km at ~21°N. North of 22°N, the HV2 appears to detach from the HV1. HV1 and HV2 likely represent the subducted Indian oceanic slab based on previous geochemical results and their morphology. The anomaly beneath the eastern boundary of the western Myanmar block (HV3) shows subparallel to the HV1 and velocity perturbations of 1.0 to 2.5% to a depth of ~300 km. By combining geological and paleomagnetic observations, we tended to interpret this anomaly as a remnant of another Neo-Tethyan oceanic slab that subducted ~40 million years ago. The seismic image provides significant observational evidence for the double subduction model of the Neo-Tethyan Ocean, and implies the inert tearing within the subducted Indian oceanic slab.

We also proposed a deep-learning-empowered earthquake location workflow and applied it to study the seismicity in Myanmar. The obtained catalog contains 1891 earthquakes with focal depths <50 km, a 2-fold increase compared to the conventional procedure. The novel catalog reveals that a roughly N-S-trending earthquake cluster near the Kabaw Fault (KBF) has segmentation characteristics. The northern section might be related to the active KBF, while the southern section might be subject to the backstop fault system of the Indian subduction. The KBF and backstop faults act as the eastern boundary to reconcile E‐W shortening in the shallow and deep crust. The middle segment of the Sagaing Fault exhibits a low b-value (0.51 ± 0.05) and can host large earthquakes.