Wastewater Wells, Geothermal Power Triggering Earthquakes
The continental U.S. experiences small earthquakes every day. But over the past few years, their numbers have been increasing. Geoscientists say the new epidemic of quakes is related to industrial wastewater being pumped into underground storage wells.
Now there's new research that reveals two trigger mechanisms that may be setting off these wastewater quakes — other, larger earthquakes (some as far away as Indonesia), and the activity at geothermal power plants.
Most of these little quakes in the U.S. are too small to feel. They tend to happen in "swarms." Over the past year, geoscientists traced some of these swarms to underground faults near deep wells that are often filled with waste fluid from the oil and gas drilling boom.
Nicholas van der Elst, a geophysicist with Columbia University's Lamont Doherty Earth Observatory, says there are lots of small faults all over the country. The injection of fluids migrates in and around the fault itself, "and kind of pushes outward on the fault walls and makes it easier for the fault to slip," he says.
The wastewater "loads up" these faults with tension until, at some point, they slip and the earth moves.
So what van der Elst wanted to know was: "What prompts that slip?" Sometimes it's just all that water building up. However, he discovered that in three cases in the past decade — in Oklahoma, in Colorado and in Texas — the trigger was yet another earthquake, a really big one, thousands of miles away. In each case, the large earthquakes set up large seismic waves that traveled around the surface of the earth "kind of like ripples," van der Elst says. "You can even see them on seismometers, going around the world multiple times."
Those three big quakes rang the planet like a bell. And when their seismic waves reached underground faults near waste wells in those three states, they nudged the tension in the faults past the brink. Soon, the area near the wells was swarming with mini-quakes.
And some of those swarms eventually culminated in pretty big temblors — in the magnitude-4.0 to -5.0, which is big enough to do some damage.
Van der Elst's findings appear in this week's issue of the journal Science. In the same issue, geoscientist Emily Brodsky at the University of California, Santa Cruz, reports yet another trigger mechanism for mini-quakes: the production of geothermal energy.
The power plant in question, near Southern California's Salton Sea, extracts hot water from beneath Earth's surface and turns it to steam to make electricity, then returns most of it underground. "What we found," Brodsky says, "is that the earthquake rate correlates quite strongly with the extraction of water from the field" underground.
On average, extracting half a billion gallons of water per month resulted in one detectable earthquake every 11 days.
Now, scientists have known that geothermal power plants cycling water from underground can cause small quakes. But Brodsky's research actually matches the amount of water moved to the frequency of the quakes.
These quakes are very small, she notes. But it concerns her that the geothermal plant she studied is near the southern tip of California's San Andreas fault — the source of many of the state's biggest temblors. "We ought to know what's happening on the southernmost terminus of the San Andreas fault," she says. "Of various places in the world to induce earthquakes, this is a particularly sensitive one."
Brodsky says it's unlikely that the geothermal plant could induce a major quake on the fault, but it's theoretically possible. The chance is more than zero, she says, but she doesn't know what the real risk is; that's what she wants to find out next.
The company that owns the plant, Mid-American Energy Holdings, declined to comment on the research.
The U.S. Geological Survey's William Ellsworth has been in the thick of this science. "One of the major questions we're concerned about," he says, "is, 'How large might an induced earthquake be?' We don't have the answer to that, and it's one of the keys to being able to better forecast the seismic hazard going forward." Ellsworth says geologists need more seismic-monitoring stations and more data from waste wells and geothermal plants to figure out the risk.
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Maji ya taka, visima vya maji machafu, na nishati ya joto la dunia husababisha matetemeko ya ardhi Marekani inakabiliwa na matetemeko madogo ya ardhi kila siku. Lakini katika miaka michache iliyopita, idadi yao imekuwa ikiongezeka. Wataalamu wa sayari wanasema kwamba tetemeko hilo la ardhi linatokana na maji machafu yanayotokana na viwanda yanayopakiwa kwenye visima vya chini ya ardhi. Utafiti mpya unafunua njia mbili za kuchochea tetemeko la maji machafu, tetemeko lingine kubwa (nengine ziko mbali kama Indonesia) na shughuli za mitambo ya umeme wa joto la ardhi. Matetemeko mengi ya ardhi nchini Marekani ni madogo sana hivi kwamba hayawezi kuhisi. Wao huwa na "maambukizi". Katika mwaka uliopita, wanasayansi wa kijiolojia walipata baadhi ya makundi hayo katika mapengo ya chini ya ardhi karibu na visima vya kina kirefu ambavyo mara nyingi hujazwa na maji ya taka kutoka kwa mashine za kuchimba mafuta na gesi. Nicholas van der Elst, mtaalamu wa jiolojia wa Chuo Kikuu cha Columbia, anasema kwamba kuna maporomoko mengi ya ardhi nchini kote. "Kupiga maji huingia ndani na kuzunguka ufa huo, na kwa njia fulani huendeshwa nje kwenye kuta za ufa huo na kufanya iwe rahisi kwa ufa huo kuteleza,"" anasema." Maji ya taka "hujaza" mapungufu hayo mvutano hadi, wakati fulani, yanapoanguka na dunia kuhamia. Kwa hiyo kile ambacho van der Elst alitaka kujua kilikuwa: "Ni nini kinachosababisha kuteleza huko?" Wakati mwingine ni tu kwamba maji yote kujenga juu. Hata hivyo, aligundua kwamba katika visa vitatu katika muongo uliopita - katika Oklahoma, Colorado na Texas - kisababishi kilikuwa tetemeko jingine la ardhi, kubwa sana, maelfu ya maili mbali. Katika kila kisa, matetemeko makubwa ya ardhi yalitokeza mawimbi makubwa ya matetemeko ya ardhi ambayo yalizunguka uso wa dunia "kama mawimbi", asema van der Elst. "Hata unaweza kuyaona kwenye vipima-tetemeko vya ardhi, yakizunguka ulimwengu mara nyingi". Matetemeko hayo matatu makubwa yaliathiri sayari hiyo kama kengele. Mawimbi ya tetemeko la ardhi yalipofika kwenye maporomoko ya chini ya ardhi karibu na visima vya maji machafu katika majimbo hayo matatu, yaliongeza mvutano katika maporomoko hayo hadi kwenye ukingo wa ukingo. Punde si punde, eneo lililokuwa karibu na visima hilo likaanza kutikiswa na matetemeko madogo-madogo. Baadhi ya tetemeko hilo lilitokeza tetemeko kubwa la ardhi lenye ukubwa wa -4.0 hadi -5.0, ambalo ni kubwa vya kutosha kuleta uharibifu. Utafiti wa Van der Elst umechapishwa katika toleo la wiki hii la jarida la Science. Katika toleo hilo, mwanasayansi wa dunia Emily Brodsky wa Chuo Kikuu cha California, Santa Cruz, anaripoti kuhusu utaratibu mwingine unaosababisha matetemeko madogo ya ardhi: utengenezaji wa nishati ya joto la dunia. Kituo hicho cha umeme, kilicho karibu na bahari ya Salton, kusini mwa California, kinatoa maji ya moto kutoka chini ya ardhi na kugeuza kuwa mvuke ili kutengeneza umeme, kisha kurudisha sehemu kubwa ya maji hayo chini ya ardhi. "Brodsky anasema, ""Tuligundua kwamba kiwango cha matetemeko ya ardhi kinahusiana sana na uchimbaji wa maji kutoka kwenye shamba hilo." Kwa wastani, kuchimba lita milioni moja za maji kwa mwezi kulisababisha tetemeko la ardhi moja kila baada ya siku 11. Sasa, wanasayansi wanajua kwamba mitambo ya umeme ya joto la dunia inayotumia maji kutoka chini ya ardhi yaweza kusababisha matetemeko madogo-madogo ya ardhi. Utafiti wa Brodsky ulionyesha kwamba kiasi cha maji kilichohamishwa kilikuwa sawa na mara nyingi za matetemeko ya ardhi. Yeye asema kwamba matetemeko hayo ni madogo sana. Lakini inamsumbua kwamba kiwanda cha joto la dunia alichokichunguza kiko karibu na ncha ya kusini ya San Andreas fault ya California - chanzo cha tetemeko kubwa zaidi la ardhi katika jimbo hilo. "Tunapaswa kujua kinachotokea kwenye mwisho wa kusini kabisa wa ufa wa San Andreas", asema. "Kati ya maeneo mbalimbali ulimwenguni yanayosababisha matetemeko ya ardhi, hii ni mojawapo ya maeneo yenye hatari sana". Brodsky anasema ni vigumu kwamba kiwanda cha joto la dunia inaweza kusababisha tetemeko kubwa juu ya kosa, lakini ni uwezekano wa kinadharia. """Uwezekano ni zaidi ya sifuri,"" anasema, ""lakini sijui hatari halisi ni nini, hiyo ndiyo anataka kujua baadaye.""" Kampuni inayomilikiwa na kiwanda hicho, Mid-American Energy Holdings, ilikataa kutoa maoni juu ya utafiti huo. William Ellsworth, mtafiti wa Marekani wa kijiolojia, aliandika hivi: "Mmoja wa maswali makuu tunayohangaikia", asema, "ni, 'Tetemeko la ardhi linaloweza kusababishwa na umeme linaweza kuwa kubwa kadiri gani?' "Hatujui jibu la swali hili, na ni muhimu sana kuweza kutabiri hatari ya tetemeko la ardhi.""" "Ellsworth anasema wanjiolojia wanahitaji vituo zaidi vya ufuatiliaji wa tetemeko la ardhi na data zaidi kutoka kwa visima vya taka na mitambo ya joto la ardhi ili kujua hatari.""" Copyright: NPR Kwa maelezo zaidi, tembelea www.nl.org.