Ring of Fire

No, not that one. It’s an awesome song by an incredible artist.

 

But we are SOS California. So if we’re talking about natural oil and gas seeps and the Ring of Fire, you can guess that we are talking about…earthquakes.

 

Yeah… THAT Ring of Fire.

 

And it’s been in the news a lot lately. There’s been what seems to be an unusual amount of activity in areas that fall under that designation.

But what is it really, and how did it come to be named after a Johnny Cash song?
Kidding…johny-cash-ring-of-fire

 

We all know that the Santa Barbara Channel…well, ALL of California…is an area that is prone to earthquakes. That is because we are on the Ring of Fire. Do you also know that earthquakes can cause big increases in seep flow? No one likes an oil spill, but historical accounts indicate that an oil spill is what has happened during earthquake activity. AND oil and gas production, by reducing seep quantities, can reduce the risk of an increased seep associated with seismic shaking. It all will come full circle (full ring?) back to seeps. Really. Keep reading.

 

As defined by the National Geographic Society, the Ring of Fire is a string of volcanoes and sites of seismic activity, or earthquakes, around the edge of the Pacific Ocean. Roughly 90 percent of all earthquakes occur along the Ring of Fire, as do 75 percent of all active volcanoes on Earth (hence the fire reference). More a 40,000-kilometer (25,000-mile) horseshoe than a ring, it stretches from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan, and into New Zealand.

 

To understand why this is such a geologically active area, it helps to know a bit about plate tectonics. As described by the National Oceanic and Atmospheric Administration’s (NOAA’s) Ocean Service, the Earth is in a constant state of change. Earth’s crust, called the lithosphere, consists of 15 to 20 moving tectonic plates. Earth’s land masses move toward and away from each other at an average rate of about 0.6 inch a year. Some regions, such as coastal California, move quite fast in geologic terms — almost 2 inches each year — relative to the more stable interior of the continental United States. At the “seams” where tectonic plates come in contact, the crustal rocks may grind violently against each other, causing earthquakes and volcanic eruptions. The Ring of Fire is where the Pacific Plate meets many plates, including our own North American Plate.

 

Since we arring-of-fire-mape part of this Ring of Fire, when it gets active, we get interested…and we check with the US Geological Survey (USGS). In the past month or so, 12 of the 14 major earthquakes have been on the Ring of Fire, including these five on our side of the Pacific:  6.1 – 17km SSE of Matias Romero, Mexico; 7.1 – 1km ESE of Ayutla, Mexico; 3.6 – 5km NW of Westwood, CA and (September 19); 3.3 – 3km NNE of East Foothills, California (September 15); and 8.1 -100km SW of Tres Picos, Mexico (September 8).

 

The relatively fast movement of the tectonic plates under California explains the frequent earthquakes that occur here. The San Andreas Fault is one of the most active faults on the Ring of Fire. But we don’t have to wait for a “big one” from that famous fault. The Santa Barbara Channel is plenty active on its own. In its Earthquake Track, the USGS reported that the Channel has been the epicenter or in the area of detection for 0 earthquakes today (as I’m writing this blog), 3 earthquakes in the last month, and 57 in the last year.  The most significant in the past month was a magnitude 2.6 centered near Oak View and, in the past year, was a magnitude 4.1 centered in Isla Vista.

 

But what is the connection between seismicity and seeps? Some historical examples include:

  • The Santa Barbara Daily News, in its July 4, 1925, edition, reported that W.H. Schuyler, crossing the channel from Santa Cruz Island, noted “Gaping oil fissures crisscross the channel between Santa Barbara and the Channel Islands since the great quake of last Monday have been pouring their oil contents into the sea.”
  • An increase in natural oil seepage was noted after the 6.5 magnitude Sylmar quake in 1971, and following a small Ventura event.
  • An onshore petroleum seep in the Ojai Valley, California developed as a direct result of the 1994 Northridge earthquake.

This all relates to the Ring of Fire.

 

A recent report from UC Santa Barbara (UCSB) provides another example. Starting in March 1978 and continuing sporadically through July 1978, a swarm of small earthquakes–called microearthquakes– occurred underneath the northeastern end of the Santa Barbara Channel., Santa Barbara residents complained of an unusually large amount of oil and tar on local beaches in July and early August. A magnitude 5.2 earthquake shook the channel on August 13, 1978.

Arco was producing oil and gas and monitoring seep volume via fabric devices that pre-dated the seep tents, which were installed in 1982. They reported an increase in seep volume prior to the 1978 earthquake.

 

Why would the action of an earthquake release a seemingly increased volume of natural seepage?

Is the shaking enough to open cracks that are deep enough to access the very formations from which the oil is seeping? Not exactly.

 

Jim Boles is an Emeritus Professor of Geology, Department of Earth Science at UCSB. As he describesmap-of-oil-seeps in his study entitled Hydrocarbon Production from the South Ellwood Oil Field (Platform Holly) and the Effects on Naturally Occurring Oil and Gas Seeps, seep oil and gas rise from the formations in which they are pooled to the ocean floor through small pores and fractures. The accumulation of the oil and gas gives the hydrocarbon buoyancy to overcome the drag from contact with small openings in the rock (fractures, pores, etc).  Seismic shaking serves to help the hydrocarbon overcome the drag forces. The amount of oil and gas that floats toward the seafloor is dependent on the formation pressure as compared to the pressure from a full ocean of water trying to push it back in. Oil and gas production reduces the pressure in the formation, so it takes less pressure from above to hold the oil and gas back, even though oil and gas are still in the cracks and pores.

 

Seismic motion in the area of an active seep could, in effect, “break the seal” that holds the oil back. Picture a bottle of Coke – it’s a quiet and closed system until shaken. The shaking would loosen any oil and gas sticking to rock in the small fractures, and disrupt the boundary between seawater and oil within those fissures.

 

So instead of opening cracks, the phenomenon would be more of oil seeping from existing seafloor sources. As the shaking stops, the releases would eventually as well. This would explain increased seepage and an increase before an earthquake occurs.

 

We have some updated information on earthquake risk along our coast. A study of the Ventura-Pitas Point Fault, published in Geophysical Research Letters, confirms that the structure of this fault brings it closer to the surface than originally thought, which increases the risk of a stronger quake.

 

As Dr. Boles’ study concluded, there is clear scientific evidence that hydrocarbon production has reduced naturally occurring oil and gas seepage in the surrounding areas. Removal of hydrocarbon reduces the amount of oil and gas available for seepage, and also results in a reduction in the driving force for hydrocarbon escape. Furthermore, the rate of hydrocarbon extraction from producing wells far exceeds the rate of natural hydrocarbon generation, migration, and accumulation. As a result, reservoir fluid pressure is reduced and the rate of seepage decreases due to the pressure reduction.

 

Since Platform Holly was shut down after the Refugio spill, we’ve been hearing more and more reports from surfers and offshore workers about increased seep and tar accumulation offshore…in the absence of a major earthquake. The bottom line is that active production of the underlying oil and gas reserves reduces the risk of a spontaneous gush oil and gas that could be produced from any seismic shaking. Platform Holly has not been decommissioned yet. Can we afford to let this opportunity to protect our offshore and coastal environment from chronic pollution – and from a significant release that could come from a seismic event?

 

There are many ways to be prepared.