Mid-crustal weak zone characterized by low velocity and resistivity in the Guangdong-Hong Kong-Macao Greater Bay Area

The seismic hazard in the economically vital Guangdong–Hong Kong–Macao Greater Bay Area (GBA) may be underestimated due to limited constraints on deep crustal structure beneath this intraplate region. Imaging the crust using complementary geophysical parameters is essential for understanding the mechanical state of the lithosphere and its role in earthquake processes. To complement existing regional shear-wave velocity models, we conducted a ∼100-km-long high-resolution magnetotelluric (MT) transect across the western flank of the Pearl River Delta. The resulting resistivity model reveals multiple crustal low-resistivity zones interpreted as fluid-rich or partially molten domains. These conductive anomalies show good spatial correspondence with previously reported low shear-wave velocity features, providing independent validation of the regional seismic structure. Our principal finding is a laterally extensive mid-crustal zone characterized by both low resistivity and low shear-wave velocity near Xinhui, Jiangmen. This anomalous body forms a mechanically weak domain embedded beneath a comparatively rigid upper crust, indicating partial mechanical decoupling between the upper and middle crust. Such a structure does not directly host earthquake rupture but may influence the mechanical environment of upper-crustal faults by facilitating stress redistribution and strain localization. These results suggest that deep crustal rheological heterogeneity plays an important role in modulating intraplate seismicity in the GBA and highlight the value of integrated MT and seismic imaging for seismic hazard assessment in continental interior and marginal regions. • A ∼100-km-long high-resolution magnetotelluric profile images the crustal resistivity structure beneath the Guangdong–Hong Kong–Macao Greater Bay Area. • A laterally continuous mid-crustal zone characterized by low resistivity and low shear-wave velocity is identified, indicating a mechanically weak domain. • Integrated geophysical evidence suggests the weak zone reflects fluid enrichment and/or localized partial melting and may influence stress distribution and upper-crustal seismicity.