Constraining the Moho Depth Below Bhutan With Global-Phase Seismic Interferometry

Anne Obermann,Irene Bianchi,Elmer Ruigrok,György Hetényi

doi:10.3389/feart.2021.658146

Abstract

We use a novel technique named global-phase seismic interferometry (GloPSI) to image the lithospheric structure, and in particular the Moho, below two parallel north-south transects belonging to the GANSSER network (2013–2014). The profiles cross the Himalayan orogenic wedge in Bhutan, a tectonically important area within the largest continent-continent collision zone on Earth that is still undergoing crustal thickening and represents a challenging imaging target for the GloPSI approach. GloPSI makes use of direct waves from distant earthquakes and receiver-side reverberations with near vertical incidence. Reflections are isolated from earthquake recordings by solving a correlation integral and are turned into a reflectivity image of the lithosphere below the arrays. Our results compare favorably with first-order features observed from a previous receiver function (RF) study. We show that a combined interpretation of GloPSI and RF results allows for a more in-depth understanding of the lithospheric structure across the orogenic wedge in Bhutan.

Highlights

The temporary passive seismic experiment GANSSER (Geodynamics ANd Seismic Structure of the Eastern Himalaya Region) continuously recorded seismic data from a total of 37 broadband stations in Bhutan from January 2013 to November 2014
The first step is the application of seismic interferometry, which for global-phase seismic interferometry (GloPSI), amounts to the autocorrelation and stacking of selected time windows, and the flipping of the amplitudes (Figures 3 A1, B1)
Average removal was not needed in Bianchi et al (2021) who applied GloPSI to an array that was deployed for a similar duration

Summary

Introduction

The temporary passive seismic experiment GANSSER (Geodynamics ANd Seismic Structure of the Eastern Himalaya Region) continuously recorded seismic data from a total of 37 broadband stations in Bhutan from January 2013 to November 2014. Bhutan’s structural segment boundaries within the Himalayas are highlighted both by gravity anomaly residuals and by orogen-crossing mid- to lower crustal seismicity of the underthrusting plate (Hammer et al, 2013; Hetenyi et al, 2016a; Diehl et al, 2017). Both the Bhutan Himalayas and the Shillong Plateau can accommodate great earthquakes, as witnessed by the 1714 and 1897 events, respectively (Bilham and England, 2001; Berthet et al, 2014; Hetenyi et al, 2016b, 2018; Le Roux-Mallouf et al, 2016). As demonstrated by Coulomb stress modeling, the two regions are seismotectonically less linked than previously proposed (Grujic et al, 2018)

Methods

Results

Conclusion