What is an earthquake precursor? What are the common precursors?

The first question: earthquake precursors refer to abnormal phenomena before earthquakes. Under the action of in-situ stress, in the process of stress and strain gradually accumulating and strengthening, rock mass will cause the occurrence of materials around the source, such as geophysical anomalies such as seismic activity, obvious surface changes, geomagnetism, geoelectricity and gravity, as well as abnormal behaviors of groundwater level, hydrochemistry and animals. Generally speaking, these abnormal changes related to the preparation and occurrence of earthquakes are called earthquake precursors (also known as earthquake anomalies). It includes microscopic earthquake anomalies and macroscopic earthquake anomalies.

The second problem: the main anomalies are turbidity, bubbling, flowering, temperature rise, discoloration, odor, sudden rise, sudden drop, borehole deformation, sudden exhaustion or gushing of spring water, etc.

Pigs don't enter the circle, don't eat, make a hullabaloo about, and the arch crosses the circle.

Dogs bark endlessly, cry, sniff, bite, run around, move around with puppies in their mouths, and police dogs don't listen to instructions.