Nature and Energy Source of the Strong Waveforms Recorded during the 2008 Wenchuan Earthquake

TL;DR

This paper investigates the energy sources of the 2008 Wenchuan Earthquake, proposing that fluid pressure release from reservoirs in sedimentary strata significantly contributed to the earthquake's energy, beyond fault dislocation alone.

Contribution

It introduces the idea that fluid pressure release in reservoirs is a major energy source for large earthquakes, supported by waveform analysis and geological evidence.

Findings

Seismic wave characteristics suggest non-S-wave energy contributions.

Fluid pressure release can match energy levels of magnitude 8.0 earthquakes.

Evidence from seismic data and drilling indicates fluid involvement in seismic events.

Abstract

Earthquakes are indeed triggered by fault dislocations, but whether this process alone can produce the actual earthquake energy released by the mainshock has long been questioned. Therefore, exploring the true source of energy that causes earthquakes after the first motion is necessary. Based on analyses of the waveforms and ray paths at seismic stations close to the epicenter, it is considered that strong earthquake vibrations may not be caused by S-waves. It is also proposed that the reservoirs in sedimentary strata contain large amounts of high-pressure fluids, whose pressures can be released under certain conditions; this release of pressure may be an important component of the main earthquake energy. When a natural fault ruptures and penetrates a reservoir with a large area, the elastic energy produced by the release of pressure can reach the energy released by an earthquake of magnitude 8.0. Artificial engineering activities can lead to small-scale fluid pressure release phenomena, such as blowouts during drilling and earthquakes induced by hydraulic fracturing. Much direct and indirect evidence, such as the characteristics of seismic waves in the time and frequency domains recorded during the Wenchuan earthquake, explosion phenomena observed on the ground and cores obtained by scientific drilling, indicates the possibility of such energy release. We propose that seismicity can be divided into three stages: the microfracturing stage, in which there is fluid activity and can produce an electrokinetic effect; the significant fracturing stage after the initial movement; and the strong earthquake stage caused by fluid pressure release.