Electromagnetic Anomalies around The Wenchuan Earthquake and Their Relationship with Earthquake Preparation

Table 1

Summary of electromagnetic precursors before the Wenchuan earthquake.

Type of electromagnetic precursors	Parameters
Long-term anomaly more than 1 year	Apparent resistivity; OLR; electromagnetic emissions in near epicentral area
Midterm anomaly in a few months	Geomagnetic field; electromagnetic emissions; thermal infrared; SNR of VLF transmitter
Imminent anomaly in a few days	GPS TEC; plasma parameters; VLF electric field in ionosphere; foF2, ELF electromagnetic field
Anomaly in a few hours	No found