Tag Archives: induced seismicity

Has That Oilfield Caused My Earthquake?

“Some six months have passed since the magnitude (Mw) 6.7 earthquake struck Los Angeles County, with an epicenter close to the coast in Long Beach. Total economic loss estimates are more than $30 billion.  Among the affected homeowners, the earthquake insurance take-up rates were pitifully low – around 14 percent. And even then, the punitive deductibles contained in their policies means that homeowners may only recover 20 percent of their repair bills.  So, there is a lot of uninsured loss looking for compensation. Now there are billboards with pictures of smiling lawyers inviting disgruntled homeowners to become part of class action lawsuits, directed at several oilfield operators located close to the fault. For there is enough of an argument to suggest that this earthquake was triggered by human activities.”   

This is not a wild hypothesis with little chance of establishing liability, or the lawyers would not be investing in the opportunity. There are currently three thousand active oil wells in Los Angeles County. There is even an oil derrick in the grounds of Beverly Hills High School. Los Angeles County is second only to its northerly neighbor Kern County in terms of current levels of oil production in California.  In 2013, the U.S. Geological Survey (USGS) estimated there were 900 million barrels of oil still to be extracted from the coastal Wilmington Field which extends for around six miles (10 km) around Long Beach, from Carson to the Belmont Shore.

Beverly Hills High School Picture Credit: Sarah Craig for Faces of Fracking / FLICKR

Beverly Hills High School   Picture Credit: Sarah Craig for Faces of Fracking / FLICKR

However, the Los Angeles oil boom was back in the 1920s when most of the large fields were first discovered. Two seismologists at the USGS have now searched back through the records of earthquakes and oil field production – and arrived at a startling conclusion. Many of the earthquakes during this period appear to have been triggered by neighboring oil field production.

The Mw4.9 earthquake of June 22, 1920 had a shallow source that caused significant damage in a small area just a mile to the west of Inglewood. Local exploration wells releasing oil and gas pressures had been drilled at this location in the months before the earthquake.

A Mw4.3 earthquake in July 1929 at Whittier, some four miles (6 km) southwest of downtown Los Angeles, had a source close to the Santa Fe Springs oil field; one of the top producers through the 1920s, a field which had been drilled deeper and had a production boom in the months leading up to the earthquake.

A Mw5 earthquake occurred close to Santa Monica on August 31, 1930, in the vicinity of the Playa del Rey oilfield at Venice, California, a field first identified in December 1929 with production ramping up to four million barrels over the second half of 1930.

The epicenter of the Mw6.4 1933 Long Beach earthquake, on the Newport-Inglewood Fault was in the footprint of the Huntingdon Beach oilfield at the southern end of this 47 mile-long (75 km) fault.

As for a mechanism – the Groningen gas field in the Netherlands, shows how earthquakes can be triggered simply by the extraction of oil and gas, as reductions in load and compaction cause faults to break.

More Deep Waste Water Disposal Wells in California than Oklahoma

Today many of the Los Angeles oilfields are being managed through secondary recovery – pumping water into the reservoir to flush out the oil. In which case, we have an additional potential mechanism to generate earthquakes – raising deep fluid pressures – as currently experienced in Oklahoma. And Oklahoma is not even the number one U.S. state for deep waste water disposal. Between 2010 and 2013 there were 9,900 active deep waste water disposal wells in California relative to 8,600 in Oklahoma. And the California wells tend to be deeper.

More than 75 percent of the state’s oil production and more than 80 percent of all injection wells are in Kern County, central California, which happens to be close to the largest earthquake in the region over the past century on the White Wolf Fault: Mw7.3 in 1952. In 2005, there was an abrupt increase in the rates of waste water injection close to the White Wolf Fault, which was followed by an unprecedented swarm of four earthquakes over Magnitude 4 on the same day in September 2005. The injection and the seismicity have been linked in a research paper by Caltech and University of Southern California seismologists published in 2016. One neighboring well, delivering 57,000 cubic meters of waste water each month, was started just five months before the earthquake swarm broke out. The seismologists found a smoking gun, a pattern of smaller shocks migrating from the site of the well to the location of the earthquake cluster.

To summarize – we know that raising fluid pressures at depth can cause earthquakes, as is the case in Oklahoma, and also in Kern County, CA. We know there is circumstantial evidence for a connection between specific damaging earthquakes and oil extraction in southern California in the 1920s and 1930s. According to the location of the next major earthquake in southern or central California, there is a reasonable probability there will be an actively managed oilfield or waste water well in the vicinity.

Whoever is holding the liability cover for that operator may need some deep pockets.

How should manmade earthquakes be included in earthquake hazard models?

Oklahoma, Colorado, and Texas have all experienced unusually large earthquakes in the past few years and more earthquakes over magnitude 3 than ever before.

Over a similar time frame, domestic oil and gas production near these locations also increased. Could these earthquakes have been induced by human activity?

Figure 1: The cumulative number of earthquakes (solid line) is much greater than expected for a constant rate (dashed line). Source: USGS

According to detailed case studies of several earthquakes, fluids injected deep into the ground are likely a contributing factor – but there is no definitive causal link between oil and gas production and increased earthquake rates.

These larger, possibly induced, earthquakes are associated with the disposal of wastewater from oil and gas extraction. Wastewater can include brine extracted during traditional oil production or hydraulic fracturing (“fracking”) flowback fluids – and injecting this wastewater into a deep underground rock layer provides a convenient disposal option.

In some cases, these fluids could travel into deeper rock layers, reduce frictional forces just enough for pre-existing faults to slip, and thereby induce larger earthquakes that may not otherwise have occurred. The 2011 Mw 5.6 Prague, Oklahoma earthquake and other recent large midcontinent earthquakes were located near high volume wastewater injection wells and provide support for this model.

However, this is not a simple case of cause and effect. Approximately 30,000 wastewater disposal wells are presently operated in the United States, but most of these do not have nearby earthquakes large enough to be of concern. Other wells used for fracking are associated with micro-earthquakes, but these events are also typically too small to be felt.

To model hazard and risk in areas with increased earthquake rates, we have to make several decisions based on limited information:

  • What is the largest earthquake expected? Is the volume or rate of injection linked to this magnitude?
  • Will the future rate of earthquakes in these regions increase, stay the same, or decrease?
  • Will future earthquakes be located near previous earthquakes, or might seismicity shift in location as time passes?

Induced seismicity is a hot topic of research and figuring out ways to model earthquake hazard and possibly reduce the likeliness of large induced earthquakes has major implications for public safety.

From an insurance perspective, it is important to note that if there is suspicion that the earthquake was induced, it will be argued to fall under the liability insurance of the deep well operator and not the “act of God” earthquake coverage of a property insurer. Earthquake models should distinguish between events that are “natural” and those that are “induced” since these two events may be paid out of different insurance policies.

The current USGS National Seismic Hazard Maps exclude increased earthquake rates in 14 midcontinent zones, but the USGS is developing a separate seismic hazard model to represent these earthquakes. In November 2014, the USGS and the Oklahoma Geological Survey held a workshop to gather input on model methodology. No final decisions have been announced at this time, but one possible approach may be to model these regions as background seismicity and use a logic tree to incorporate all possibilities for maximum earthquake magnitude, changing rates, and spatial footprint.

Figure 2: USGS 2014 Hazard Map, including zones where possibly induced earthquakes have been removed. Source: USGS