Spectral centroid ground motion amplitude anomaly before the Ms 8.0 Wenchuan earthquake

Abstract

At 14:28 on May 12, 2008 (Bei**g time), Wenchuan, in the Sichuan Province of China, experienced a Ms 8.0 earthquake. To investigate the spectral centroid amplitude changes that occurred before and during this earthquake, we gathered data from ten seismic stations located near the Longmenshan fault zone from May 1, 2008, to May 12, 2008. After using FFT to isolate the hourly seismic data, we then calculated the spectral centroid amplitudes in the 0.1–0.5 Hz frequency band. Overall, the spectral centroid amplitude had increased dramatically since May 10; the most anomalous amplitude increase, which likely preceded the actual seismic event itself, was recorded at YZP, the station closest to the epicenter. Once the earthquake initiated, we observed the strongest ground motion in the vertical and north-south directions along the Longmenshan fault. To further constrain any changes that occurred prior to the earthquake, we applied multi-scale wavelet decomposition to geomagnetic data collected from April 4 to May 12. The geomagnetic anomalies we found in this data correspond temporally with the spectral centroid amplitude anomalies. Based on these analyses, we inferred that the Wenchuan earthquake was driven by stress accumulation due to the compression of the Longmenshan fault system by the Bayankala Block to the west and deep obstruction by the hard basement material of the Sichuan Basin to the east. Our results agree with other investigations of the Wenchuan earthquake. We believe that the spectral centroid amplitude method is an effective and reliable technique for extracting anomaly data prior to the onset of great earthquakes, and that it can provide insight into the dynamic seismogenic process.