Large-scale deformation caused by dyke intrusion beneath eastern Hainan Island, China observed using InSAR

• InSAR images reveal large-scale deformation at eastern Hainan Island, China.
• The deformation pattern appears as a trough extending N–S.
• Small earthquakes occur in a N–S trending belt, mimicking the deformation pattern.
• An almost vertical dyke of 54 km by 1 km at 25 km depth fits the deformation.
• Small earthquakes located above the tip of the dyke accompany the intrusion.

Ground surface deformation monitoring is important for understanding regional crustal movement. However, in eastern Hainan Island, China, few near-field geodetic observations are available; thus, the in situ crustal movement remains poorly understood. In this study, the deformation field of the eastern Hainan Island region was captured from 2007 to 2011 by applying the stacking-InSAR approach to ALOS PALSAR images. The results exhibit a trough deformation pattern that extends along the small to moderate earthquake belt with a maximum peak-to-trough range change rate of approximately 9 mm/year. We propose that a magma-fed dyke is responsible for the observed surface deformation pattern. The modeled dyke is approximately 54 km long, 1 km wide, dipping 71° to the west, centered 25 km fixed during modeling beneath eastern Hainan Island, and strikes nearly N–S, parallel to the elongated pattern of seismicity in the area. We infer that the regional stress field favors the formation of dyke beneath eastern Hainan Island; consequently, the intruding magma has accumulated in an elongated, dyke-like storage zone. The zone dilated progressively over time, accompanied by sporadic earthquakes and subtle surface deformation.