The Earth is a leaky, geological geofluid system, with geo-gases like carbon dioxide and methane and also other gases like hydrogen sulfide (rotten egg smell) escaping from the Earth’s crust and mantle to the atmosphere through faults. Following the July 2019 Ridgecrest earthquake, we proposed that quakes could have stimulated geo-gas emissions through regional faults.

A unique, mobile air quality laboratory, SISTER, was used to collect atmospheric trace gas survey data and sample canister data in Searles, Panamint, and Death Valleys, documented geo-gas emissions after the earthquake and most strongly from faults. Such emissions are not reported in the literature. Surveys also were conducted in the Carrizo Plain, a semiarid valley created by and following the San Andreas Fault, where strong geo-gas emissions were identified.

We also investigated Tropomi satellite methane data, which confirmed some of the observed plumes. Tropomi data also showed enhanced methane levels that tracked the San Andreas Fault along its entire length. Enhanced Tropomi methane also was found in Death Valley and Panamint Valley, with the latter validated by in situ data around Manly Pass at the Valley’s heavily faulted southern end. Elevated carbon dioxide also was observed here, over the Manly Fault.

Another area of interest was the Ubehebe Crater Field at the north end of Death Valley, where under very high (22 m s^-1) cross winds, strong carbon dioxide, hydrogen sulfide, and sulfur dioxide plumes were observed.

Air samples for the Manly Pass and Ubehebe Crater areas showed a rich diversity of volatile organic hydrocarbon trace gases, typical for geothermal systems, beyond simple geothermal gases like methane and carbon dioxide. The carbon dioxide to methane ratio was consistent with a deep origin from a magma system rather than a shallow sedimentary geothermal origin. Ratios of methane, ethane, and propane suggested a geothermal formation for the volatile organic hydrocarbons with temperatures above 260C but cooler than magmatic system temperatures

The data suggested that geo-gases originated from deep and shallow systems in both settings, Death Valley/Panamint Valley and Carrizo Plain. In Carrizo Plain, a hand-held Helium analyzer suggested the potential for mantle gas

We documented geological greenhouse gas emissions from many locations along the faults within these deep fault systems in each of the three desert valleys we studied. If these emissions occur globally in other similar settings (and for shallower fault systems), then the geological contribution to global greenhouse budgets may be undercounted, possibly significantly

It was unexpected to find large geo-gas emissions of complex, volatile organic hydrocarbons in the “pristine” Death Valley area. These emissions are a potential natural environmental stressor, and events like the Ridgecrest quake can release large quantities, posing an additional environmental stressor to these fragile and threatened desert ecosystems by adding to stressors from climate change, urban and desert forest fire air pollution, and anthropogenic activities.

Additionally, these geogas volatile organic hydrocarbon emissions are likely in some non-desert similar settings, particularly after major quakes that open migration pathways - 30 million live near the San Andreas Fault.

Tying emissions to quakes is only possible with a monitoring capacity. We have shown the potential for monitoring and larger-area surveys from oversampled Tropomi satellite data - at least for desert systems (very homogeneous background).

Finally, we showed that in situ mobile geo-gas atmospheric emission surveys are a novel, useful tool to identify unknown faults and information about faults and geological structures. This information better informs geo-hazard assessments – assessments that underlie development regulations, insurance costs, etc.

Last Modified: 09/07/2024
Modified by: Ira Leifer