Abstract: An earthquake with M_S5.1 occurred in Wen'an County, Hebei Province in north China, on July 4, 2006. Based on monthly average Grid data with spatial resolution of 2.5°×2.5°, getting from observations of NOAA/IR polar orbit satellite in recent years, this paper analyzed the anomalous characteristics and its evolvement in time series on ambient field of OLR in north China by using Eddy covariance means before the earthquake. The research result is as follows: The change of normal ambient field is stable, the OLR value is changed with a notably anomaly two months earlier before the earthquake, and the phenomena usually happened around the epicenter. Combining previous earthquake case study by using the similar method, the characteristics of OLR anomaly before earthquake takes the catholicity. The result must have great practical significance in the short-term earthquake prediction in Northern China.

Key words: Wen′an M_S5.1 earthquake, Outgoing-Longwave-Radiation, Extraction of the anomalous information, Seismic precursor characteristics