A Shallow Shock: The 25 February 2019 ML 4.9 Earthquake in the Weiyuan Shale Gas Field in Sichuan, China by Hongfeng Yang; Pengcheng Zhou; Nan Fang; Gaohua Zhu; Wenbin Xu; Jinrong Su; Fanbao Meng; Risheng Chu, Seismological Research Letters (2020). DOI: 10.1785/0220200202
The complete paper.
Earthquakes rarely occur at extremely shallow depths, for example, less than 2 km. Even for induced earthquakes that are typically shallower than tectonic events, only very small ones have been reported in such depths. The MLML 4.9 earthquake (MwMw 4.3) that struck the Rongxian County, Sichuan, China on 25 February 2019 was an extremely shallow event. Seismological and geodetic data constrained the mainshock depth at ∼1 km∼1 km with a thrust‐faulting mechanism, consistent with the Molin fault orienting northwest. Two foreshocks with magnitudes larger than 4 occurred on an unmapped fault striking northeast, right next to an injection well where hydraulic fracturing (HF) was conducted. The focal depths of the two foreshocks were at ∼2.7 km∼2.7 km, coinciding with the depth of HF. Coulomb failure stresses of the two foreshocks on the Molin fault was ∼3 kPa∼3 kPa, smaller than typical static triggering threshold (10 kPa), and thus their triggering effects were mild. As the fault was hydraulically sealed from HF, we suggested that the MLML 4.9 earthquake was possibly triggered by nearby HF activities through poroelastic stress transfer. Such findings held significant implications for shale gas development by considering seismic hazard associated with shallow faults. …
Figure 1. Surging earthquakes in the Sichuan basin.
(a) Seismicity with local magnitudes larger than 1 since December 2008 are shown by black circles. White lines represent mapped faults. Blue focal mechanism plots denote moment tensor solutions of induced earthquakes in the Changning region (Leiet al., 2017, 2019a). Red focal mechanism plot indicates the 25 February 2019 Mw 4.3 (ML 4.9) earthquake. WYSF, Weiyuan shale gas field. Inset shows the location of the study region.
(b) Daily number of earthquakes (ML > 1) in the Rongxian–Weiyuan region with location shown in (a) by the red dashed lines. Red line denotes seismic moment release (converted from ML = 1:3Mw − 0:88 that was empirically estimated in the region) from December 2008 to March Red dot marks the occurrence time of the 25 February 2019 mainshock. The color version of this figure is available only in the electronic edition.
… By far, the largest HF triggered earthquake (the 2018 Xingwen earthquake with a local magnitude ML 5.7) occurred in the southern Sichuan basin (Lei et al., 2019a), where the Changning–Weiyuan shale gas block (Fig. 1a) had been discovered and developed since 2011.
A few other Mw > 4 earthquakes had been linked with HF in the Changning shale gas block, including five ML 4–5 earthquakes in 2017 (Lei et al., 2017; Meng et al., 2019) and an ML 5.3 earthquake in 2019 (Lei et al., 2019a). In addition to HF triggered earthquakes, fluid injection
for salt mining in the Changning area had been conducted for three decades, which possibly led to an Mw 6.0 earthquake in June 2019 (Lei et al., 2019b).
In contrast, the Rongxian–Weiyuan region, located ∼150 km north of Changning, had infrequent seismicity with ML larger than 1 before mid-2015 (Fig. 1b). Then, earthquakes
occurred more often, but the magnitudes were up toMw 3.4 before 2018 (Lei et al., 2017). The number of earthquakes with ML > 1 increased drastically from 2018, with a few ML > 4 damaging events (Fig. 1b). On 25 February 2019, an ML 4.9 earthquake struck the region at 1:15 p.m., with a reported intensity of VI. As reported by The Paper, the earthquake caused two fatalities in the Gaoshan Town and 12 injuries, resulting in numerous damaged houses, and an estimated economic loss of 14 million RMB (∼2 million U.S.). The earthquake was preceded by two M 4+ foreshocks, one at 5:38 p.m. on 24 February and the other at 8:40 a.m. on 25 February. HF wells within 2 km to their epicenters were in operation, before the occurrences of these earthquakes. Immediately
after the mainshock, HF activities in the Rongxian County were shut down. Identifying the responsible faults of the earthquakes and finding the potential link with HF are critical not only for seismic hazard assessment in the region, but also for sustainable development of shale gas industry in China. …
Unusually shallow earthquake ruptures in Chinese fracking field by Seismological Society of America, Oct 7, 2020, phys.org
An unusually shallow earthquake triggered by hydraulic fracturing in a Chinese shale gas field could change how experts view the risks of fracking for faults that lie very near the Earth’s surface.
In the journal Seismological Research Letters, Hongfeng Yang of The Chinese University of Hong Kong and colleagues suggest that the magnitude 4.9 earthquake that struck Rongxian County, Sichuan, China on 25 February 2019 took place along a fault about one kilometer (0.6 miles) deep.
The earthquake, along with two foreshocks with magnitudes larger than 4, appear to be related to activity at nearby hydraulic fracturing wells. Although earthquakes induced by human activity such as fracking are typically more shallow than natural earthquakes, it is rare for any earthquake of this size to take place at such a shallow depth.
“Earthquakes with much smaller magnitudes, for example magnitude 2, have been reported at such shallow depths. They are understood by having small scale fractures in such depths that can slip fast,” said Yang. “However, the dimensions of earthquakes are scale-dependent. Magnitude 4 is way bigger than magnitude 2 in term of rupture length and width, and thus needs a sizeable fault as the host.”
“The results here certainly changed our view in that a shallow fault can indeed slip seismically,” he added. “Therefore, we should reconsider our strategies of evaluating seismic risk for shallow faults.”
Two people died and twelve were injured in the 25 February earthquake, and the economic loss due to the event has been estimated at 14 million RMB, or about $2 million. There have been few historic earthquakes in the region, and before 2019 there had been no earthquakes larger than magnitude 3 on the fault where the main earthquake took place.
Since 2018, there have been at least 48 horizontal fracking wells drilled from 13 well pads in the region, with three well pads less than two kilometers (1.2 miles) from the Molin fault, where the main earthquake took place.
Yang and his colleagues located the earthquakes and were able to calculate the length of the main rupture using local and regional seismic network data, as well as InSAR satellite data.
It is unusual to see clear satellite data for a small earthquake like this, Yang said. “InSAR data are critical to determine the depth and accurate location of the mainshock, because the ground deformation was clearly captured by satellite images,” he noted. “Given the relatively small size of the mainshock, it would not be able to cause deformation above the ‘noise’ level of satellite data if it were deeper than about two kilometers.”
The two foreshocks took place on a previously unmapped fault in the area, the researchers found, underscoring how difficult it can be to prevent fracking-induced earthquakes in an area where fault mapping is incomplete.
The researchers note that the Molin fault is separated from the geologic formation where fracking took place by a layer of shale about 800 meters (2625 feet) thick. The separating layer sealed off the fault from fracking fluids, so it is unlikely that the pressures of fluid injected into rock pores around the fault caused the fault to slip. Instead, Yang and colleagues suggest that changes in elastic stress in rock may have triggered the main earthquake on the Molin fault, which was presumed to be stable.
“The results here certainly pose a significant concern: we cannot ignore a shallow fault that was commonly thought to be aseismic,” Yang said, who said more public information on fracking injection volume, rate and duration could help calculate safe distances for well placement in the future.
Refer also to:
One of Canada’s foremost experts on earthquake hazards recently told an audience of Calgary engineers that earthquakes triggered by hydraulic fracturing can exceed “what the natural hazard was in the first place” and pose risks to infrastructure only built to withstand natural earthquake hazards.
As well, earthquakes induced by fracking can produce more damaging ground motion at lower magnitudes than natural quakes due to their shallowness, said Gail Atkinson, the NSERC/TransAlta/Nanometrics Industrial Research Chair in Hazards from Induced Seismicity at Ontario’s Western University.
Natural earthquakes have an average depth of 10 kilometres, whereas industry-made tremors are much shallower and closer to the ground surface where people can feel them more strongly.
Natural earthquakes typically cause structural damage in buildings at a magnitude of 5.0, Atkinson said. But earthquakes triggered by fracking could possibly cause damaging ground motions at magnitudes as low as 3.5 to 4.0, due to their shallowness. …
Industry doesn’t share data
According to Atkinson’s preliminary estimate, as many as one in five wells in the Fox Creek region may be triggering seismic activity.
Right now, scientists have no accurate way of predicting whether one-in-five horizontal wells will provoke a felt man-made earthquake, or whether one-in-1,000 wells will do so. The industry simply doesn’t know where all the faults are, nor the likelihood of triggering fault movement.
Nor do they know how large or destructive an earthquake trigged by hydraulic fracturing might be. To reduce uncertainty, Atkinson appealed for more seismic data and open access to that data, as well as timely access to operational data.
Many oil and gas companies currently collect their own seismic data, but do not share this information with the public or earthquake scientists.
“There are hundreds and hundreds of scientists working on this issue right now, but if they are not able to see the data, there is no scientific benefit from collecting it,” Atkinson said.
In Alberta, two or three years may pass before regulators report on earthquake events caused by the oil and gas industry.
… A recent talk by Usman Ahmed, the vice president of Baker Hughes, a major fracking company, highlighted the chaotic and non-linear nature of cracking shale rocks which are already under high stress.
Ahmed said that 70 per cent of unconventional wells in the U.S., even with fracking, do not met their production targets; that 60 per cent of all fracture stages are ineffective; and that 73 per cent of operators say they do not know enough about the subsurface, let alone where the faults are.
He ended his talk by asking that the industry “avoid faults and geohazards.”
A few of the comments:
The world is running out of and billions are suffering from the lack of clean drinking water, while these crooks are poisoning and pumping incredible amounts underground . Not for real economic, but fraudulent monetary reasons to enrich a few.
“Atkinson appealed for more seismic data and open access to that data, as well as timely access to operational data.
Many oil and gas companies currently collect their own seismic data, but do not share this information with the public or earthquake scientists.”
That’s not surprising, apparently that information is “proprietary,” just like the secret chemicals companies are injecting.
“Many researchers also repeatedly raised the issue of access to quality data, a clear necessity to advance the science. Larger events detected on national arrays are available through open databases, enabling researchers to develop new processing techniques such as signal matching to revisit data sets to find weaker, undetected background seismicity.
In many cases, companies are installing their own proprietary local arrays, which provide unique and much more sensitive recording to obtain a more complete seismic data set.
Even in the case of open data sets, there is a clear need for complimentary reservoir engineering data including reliable records of injection volumes, rates, and pressures that are often lacking. Long-term data related to stress and strains before, during, and after injection are also missing pieces of the puzzle.”
“These man-made events are so much more frequent in a low seismic area such as Fox Creek and most of Alberta that they could challenge the adequacy of current seismic hazard assessments now used to set current building and critical infrastructure codes.
‘In low seismic environments like Fox Creek where the natural earthquakes are infrequent, the hazards from an induced seismic event can exceed the hazards from a natural source,’ warned Atkinson.”
I sincerely hope the residents of Fox Creek (and everywhere else companies are frac’ing) are documenting daily the state of their homes, outbuildings, offices, infrastructure etc, because you just never know when you and your town are going to be “in the wrong place at the wrong time.”
And things like, “a number of water main breaks” or declining water levels, should definitely be scrutinized and coordinated with further scrutiny of the “proprietary” data companies refuse to provide.
“We understand that there have been issues with the discolouration of the water in Town lately. Due to recent events (which include the recent fire and a number of water main breaks) the Town has not been able to catch up properly on the required water levels.”
At the end of the day, regardless of whether we work in the industry or not, worship the industry or not, or have promised our first deformed child to the industry or not, we are fools to expect anything more than the complete and utter destruction of our communities, as long as this industry is allowed to continue to run amok.
“The fears of residents have not been assuaged by comments from Chiel Seinen, the spokesman for the Nederlandse Aardolie Maatschappij (NAM), a gas consortium including Royal Dutch Shell Plc and Exxon Mobil Corp, who conceded that people’s lives might be in danger.
‘You can never exclude anything if people are in the wrong place at the wrong time,’ he told the BBC last month.”
Thank you Dr. Atkinson, you are an incredibly bright scientific light in this dark and dismal resource tunnel, I just wish there were more of you. Please keep going.
2016: Questerre’s partner to frac Quebec is Repsol, creator of 4.8M world record frackquake, day of Ernst vs AER Supreme Court of Canada hearing. “The Alberta Model” Knocks Quebec’s People to their Knees: Gov’t of Quebec Takes Your Land & Rights, Gives Them to the Frackers – For Free
2017: Fox Creek, Alberta Frac Quakes start up again; New Study by Standford Scientists: Small earthquakes at frac sites may be early indicators of bigger quakes to come; Surprising Finding: Arkansas earthquakes mostly caused by hydraulic fracturing, only some by wastewater injection, None caused by trucks
… One fracked well set off a cluster of earthquakes with magnitudes as high as 4.9 that killed two people said one report, and at least four according to another.
The tremors also damaged thousands of buildings and left hundreds homeless in Rongxian county.
In response to the quakes, thousands of angry protestors descended on government offices to demand action.
The government told the protesters it would shut down fracking operations in the region.
Seismic experts have long established that the injection of pressurized fluids into the ground over short or long periods of time can reactivate faults and cause earthquakes.
Sichuan basin, the focus of China’s shale gas fracking industry, is a densely populated area and has a grim history of tremors induced by industrial activity.
One quake triggered by the filling of dam with water, set off a massive earthquake that killed 80,000 people in 2008.
In January 2017 an earthquake triggered by China’s fracking industry damaged 571 homes.
Over the last three years fracking has triggered more than 15,000 earthquakes with magnitudes ranging up to 4.9 primarily in the Zhaotong and Changning shale gas fields of Sichuan. …
… The three earthquakes killed two people and wounded 13. More than 20,000 homes in three villages suffered damage and nine collapsed completely, according to a statement by the county. About 1,600 people were displaced….
2019: Nikiforuk: New report by BC regulator admits frac quake risk is high with formations “in a near critical state, meaning only small fluid pressure increases are sufficient to cause specific sets of fractures and faults to become critically stressed.” Researchers still can’t say where or why; Public complaints surging as frac quakes escalate. Have you read the small print of your home insurance policy?
2019: Terrifying! Injected oilfield wastewater may trigger earthquakes for ‘decades.’ More terrifying: Percentage of high-magnitude quakes felt at the surface increases with depth of waste injected & may create greater magnitude quakes years after injection rates decline or stop.
2019: 4.6M earthquake, 1 km in depth, most powerful yet in central Alberta, hits SW of Red Deer, cracks walls in homes, knocks power out to thousands. Vesta Energy reports quake to AER, shuts down frac’ing. AER investigating. Geological Survey of Canada says looks like fra’cing didn’t do it.
2020 02 23: Scrubbadubbadub! Happy Frac’ing Holidays! Two earthquakes west of Alberta’s Fox Creek Frac Hub: 4.0M on Dec 25; 4.1M on Dec 30. Like a coronavirus, it spreads. Earthquakes Canada already scrubbed the 4.1M; nothing reported in the media or by AER, again