3D Cascadia Margin (2000)

Hypothesis

In a compressional regime with accretionary ridges, fluid overpressure can build up, where gas hydrates provide an efficient seal, e.g. at elevated BSR locations. Through natural hydraulic fracturing, a slow destruction will occur while overpressure is maintained or increasing.  When the fracture reaches the surface, an ‚explosive‘ process will results due to pressure release at depth, gas falling out of solution, supporting enhanced transport of fluids and gases and heat. This heat pulse will melt locally gas hydrates in the GHSZ and generate free gas, which causes acoustic blanking in the vicinity. The system can only be episodically active, until pressure has built up again after such an event.

Observation

From a 3D high resolution seismic survey (SO 149) on the Northern Cascadia Margin in the vicinity of site, where furficial gas hydrate had been sampled, elongated blanking zones were observed in both sedment echosounder data and multichannel seismic, which align along the direction of maximum compression. 

The zone is oriented perpedicular to typical fault planes. It is located above an elevated BSR, which may allow trapping of shallow gas and building up fluid overpressure, until the gas hydrate stabilized seal is overcome by natural hydraulic fracturing.


Publication

Zühlsdorff Lars, Spiess V. (2004) Three-dimensional seismic characterization of a venting sites reveals compelling indications of natural hydraulic fracturing, Geology, 32: 101-104, https://doi.org/10.1130/G19993.1.


Master Thesis

Koletzek, Arnold (2016) Die dreidimensionale Abbildung einer Überdruckzone im Bullseye Vent am Cascadia Kontinentalrand MSc Thesis.












Nach oben