It is a debated topic if there are any observable precursor anomalies prior to the earthquake (EQ hereafter) and if the stronger EQ can be successfully predicted. During last few decades quite a lot of observable electromagnetic (EM) precursors were published by using techniques equipped in either satellites or on ground¯based stations. But there are only a few cases that the short¯term precursor anomalies of EM field before earthquakes were observed by using alternate EM fields on ground. This paper will present a new EM observation network built in recent years and show a new finding of EM field with the variation of a one¯year cycle observed using the network. As an exampleꎬ the short¯term precursor anomalies of apparent resistivity before the Yangbi EQ (Ms 5.1) occurred on March 17ꎬ 2017 in Yunnan Province will be studied. The observed anomalous phenomena indicate that the anomaly before the EQ can be captured only if a reasonably effective method is usedꎬ and it is believed that continuously observed data on the fixed observation network for a long time is an effective means for studying anomalies that appeared before earthquakes. This network can also play an important role in studying the EM environment from space.
- electromagnetic observation network
- natural EM phenomena
- precursor anomaly
- apparent restivity
- space EM environment