The significance of the high-amplitude magnetic anomaly belt in the seismotectonics of mid-west Taiwan

In mid-west Taiwan, there is a unique zone with high crustal magnetization called Lukang Magnetization High (LMH), which is believed to significantly influence earthquake activity in middle Taiwan. According to the magnetic anomaly feature in the Taiwan region, the LMH is the inversion result of the eastern part of the high-amplitude magnetic anomaly zone (NSCSMA) found in the northern South China Sea continental margin. To better understand the connection between this magnetic high (HMAZ) and background tectonic features, this study analyzes the magnetic data in mid-west Taiwan. We used wavelet spectrum analysis and compact inversion techniques to determine its causal source. Wavelet spectrum analysis results show that the wavelength of the major magnetic signal of the HMAZ is 180 km, indicating the source depth of approximately 25 km. The compact inversion results reveal high-susceptibility materials distributed around 20–30 km depth. P-wave velocity models suggest that the causal source of the HMAZ could be located in the lower crust and/or upper mantle and belong to the Eurasia plate. Based on the previous analysis results of the NSCSMA and our observation, we propose that the serpentinized materials may be the causal source of the HMAZ. Moreover, based on the regional seismicity characteristics, our findings indicate that the deformation front plays a more crucial role in the seismotectonic of mid-west Taiwan than the HMAZ.