Ambient Noise Tomography Reveals Magmatic Plumbing System Beneath the Changbaishan Volcano Field

Changbaishan volcano (CBV), located on the border between China and North Korea, has experienced multiple large-scale eruptions in the past. The well-known millennial eruption occurred in 946 and is one of the largest eruptions in the world. In 2002~2005, the CBV experienced an episode of unrest with intensive seismicity and some ground deformations, which has raised great concerns for the public. Many seismic tomography studies have been conducted in the CBV region, but due to the sparse distribution of seismic stations or smaller spatial coverage of some dense temporary stations, the crustal magma plumbing system for the CBV is still not well resolved.

To characterize the fine crustal structure of the CBV area and characterize its magmatic system, we deployed a dense seismic array over a one-month period, which consists of 277 short-period stations. The array covers an area of 200 km in the east-west direction, and 190 km in the north-south direction, with an average station spacing of 10 km. We also assembled continuous data from 14 permanent volcanic monitoring stations operated by the Jilin Earthquake Agency.

To extract high-quality empirical Green’s functions (EGFs) from one month of continuous ambient noise data, we first followed the conventional ambient noise data processing flow to compute hourly cross-correlation functions (CCFs) for each station pair. Subsequently, the template-matching-based selection method was applied to select CCFs with distinct surface wave signals for some time segments. These selected CCFs were then denoised using the SVD-based wiener filter (SVDWF) to further enhance the signal-to-noise ratios (SNRs) of CCFs. Finally, phase-weighted stacking (PWS) was employed to obtain the final CCFs for each station pair. This processing workflow significantly improved the SNRs of EGFs, enhanced the quality of the dispersion spectra and extended the surface wave dispersion frequency band from ~10 s to ~20 s.

After extracting high-quality dispersion curves, we employed the direct surface wave tomography method to invert the crustal velocity structure beneath the CBV region. The inverted Vs model reveals a prominent low-velocity anomaly in the mid-to-upper crust beneath the Tianchi crater, and the presence of a wide-spread low-velocity layer approximately 10 km thick in the middle crust. In addition, our Vs model also indicates low-velocity anomalies in the upper crust beneath the Wangtian’e crater. A unified low-velocity body connects the Tianchi crater with the Namphothe crater in the mid-to-lower crust, which suggests that these volcanic systems may originate from a common deeper source.