Characteristics and Mechanism of MBT Anomaly of Karakum Desert Related with the January 11, 2024 Hindu Kush Mw 6.4 Earthquake

The Hindu Kush locates in the seismic zone of the Tibetan Plateau at the collision region of the Eurasian plate and the Indian Ocean plate. Earthquakes are frequent here, but a few relevant studies on earthquake anomalies was found. The Mw 6.4 Hind Kush earthquake occurred on January 11, 2024, with the epicenter near the Karakum Desert. On the basis of this earthquake, this study collected the microwave brightness temperature (MBT) data from AMSR2 instrument in the research area (), so as to analyze the potential anomaly before the mainshock. The general background and random meteorological disturbance were subtracted from the original MBT images, obtaining MBT residual images during the seismogenic year by the spatio-temporally weighted two-step method.

Based on the MBT residual images at 10.65 GHz horizontal polarization, we found a significant positive MBT anomaly appeared in the eastern part of Karakum Desert, on the immediate west of the epicenter, from three days before and two days after the earthquake. The temporal characteristics of the positive MBT anomaly could be described in sequence as: pre-EQ rising, near-EQ enhancing, co-EQ peaking, after-EQ persisting and dissipating eventually. Combining the multi-source remote sensing data such as surface temperature, microwave polarization difference index, soil moisture, rainfall and snowfall, it was found that the positive MBT anomaly was influenced not only by surface temperature, but also mainly by dielectric constant changes caused by soil moisture and tectonic stresses. On January 8 (3d before the EQ), the MBT anomaly appeared in the eastern part of the Karakum Desert. Especially from January 10 (1d before the EQ) to January 13 (2d after the EQ), Soil moisture was relatively stable, but the microwave polarization difference index and MBT still showed significant anomalies. Through the multi-parameter long-term series analysis in the eastern part of the Karakum Desert, it is also confirmed that there were anomalies in MBT and dielectric constant before and after the earthquake. The deep P-hole particles activated by in-situ stress before the earthquake were transferred to the Quaternary caprock along the stress gradient, reducing the local dielectric constant. Afterwards, the microwave radiation was further amplified by the surface sand layer, ultimately leading to an increase in MBT. In addition, it was found that there were locally high CH4 concentration anomalies near the epicenter one day before the earthquake, which was probably related to the fault stress during the impending earthquake period. This study has important reference significance for identifying microwave brightness temperature anomalies during the seismogenic period and earthquake early warning in the Hindu Kush region.