One can hardly phrase it more carefully than that: "Unusual Seismic Event in North Korea". This description of what is without a doubt the fifth test of a nuclear weapon by the reclusive, authoritarian regime of Kim Jong-un in North Korea was seen on the website of the CTBTO, a United Nations organization based in Vienna, Austria. On Friday night, half an hour after midnight (UTC), seismic stations all over the world picked-up seismic waves eminating from the test site Punggye Ri in the province of North Hamgyong, located about 235 miles northeast of North Korea's capital Pyongyang. Four times since 2006, seismic waves like these were detected from the same site. Each time it turned out that these waves did not originate from a regular tectonic earthquake, but from a nuclear test conducted by North Korea. The last such test took place on January 6th of this year.
|Figure 1 A subdued headline: Diplomatic correctness did not allow the CTBTO to call a nuclear test what it really is, as seen on the organization's website shortly after the detonation|
The explosion at that time raised the question as to whether the North Koreans had tested a hydrogen bomb, which has much more destructive power than an atom bomb, like those dropped on Hiroshima and Nagasaki in the final days of World War II. The reason for this speculation - which has yet to be confirmed - was the equivalent earthquake magnitude of the detonation in January. It registered between 5.1 and 5.2. With a magnitude of 5.3, today's event was even stronger. However, the various types of nuclear weapons cannot be distinguished by seismic detection methods. That's why shortly after the latest detonation China and Japan sent "sniffer" airplanes towards the North Korean territory. They collected air samples looking for radioactive isotopes, which might have escaped during the underground nuclear test. Analyzing the composition and distribution of those isotopes would allow to uniquely identify the type of weapon tested. As of this writing, no results have been published from the analysis of air samples.
If politicians and scientists all over the world are so certain that Friday's seismic signals did not eminate from an earthquake but from the detonation of a nuclear device, why was the CTBTO so reluctant to initially call it what it really is? The reason has to do with diplomacy. The abbreviation CTBTO stands for "Comprehensive Test-Ban Treaty Organization". It took decades of careful negotiations before this organization was put in place by the UN in 1996. It has only one mandate: to monitor if a clandestine nuclear weapons test is conducted by anyone, anywhere on Earth. Now, more than 180 countries have signed that they will abide by the test-ban and have become members of CTBTO. There are, however, a few hold-outs like India, Pakistan, Cuba and North Korea. All other nations in the nuclear club (the US, Russia, China, France and the UK) have at least signed the charter, although China and the US have yet to ratify it.
And what does CTBTO do? They operate a world wide network of several hundred seismic, infrasound and hydroacoustic sensors, which can detect any nuclear test that takes place underground, in the atmosphere or at sea. In addition, at 80 stations distributed around the globe air samples are collected, similar to what the sniffer airplanes were doing shortly after today's North Korean test. The air samples of the CTBTO stations help identify the type and origin of nuclear devices.
However, CTBTO cannot operate its vast network of stations alone. It gets help from various institutions in the signatory states, among others from the Berkeley Seismological Laboratory. Our station in an abandoned mine near Yreka in Northern California, dubbed YBH, operates with a dual purpose. While YBH is an integral and important part of the Berkeley Digital Seismic Network, it also sends live seismic data to CTBTO's operations center in Vienna, Austria.
Because CTBTO is under the ultimate control of the UN Security Council, they cannot just state the obvious. Only after the member states have agreed that the data collected by CTBTO's monitoring system really represent a nuclear test, can it be called what we all know it is, another provocation of the rest of the world by Pyongyang. Since North Korea has publically admitted to the test with great propaganda fanfare, the nuclear monitors have changed their website. (hra128)
The earthquake that rattled at least seven mid-western states on Saturday morning was a stark reminder that a new type of seismic hazard exists, which is associated with human activity. The temblor with a magnitude of 5.8 was located near the town of Pawnee, about 75 miles north-northeast of Oklahoma City. Although the quake caused only minor damage, it shook an area of the United States which - until a few years ago - was considered basically free of any significant seismic activity. But ever since an earthquake with a slightly smaller magnitude struck a region immediately east of Oklahoma City in November 2011, it has become clear that a sizable seismic hazard, widely ignored until then, lurks under the oil producing states in the Midwest.
|Figure 1: Map of the seismicity in Oklahoma since 1960. The red star is the epicenter of Saturday's quake. The red dot below the star depicts the epicenter of a similar sized quake in 2011. Source: EMSC|
Since 2008, Oklahoma and neighboring states have seen a sharp increase in seismic activity. For many decades, the average rate of occurrence of quakes of magnitude 3 or larger in the Sooner State and beyond was about 3 per year. This rate is the natural background seismicity for the Midwest. However, the number changed dramatically about seven years ago, when the rate shot up to several hundred per year. In fact, currently more quakes with magnitude 3 or larger occur every year in Oklahoma than in California, the state with a highest rate of "natural," meaning tectonically driven seismicity.
When seismologists started to study the enormous increase in earthquake activity in Oklahoma, it very quickly became clear that it was not caused by natural phenomena. Instead, the cause was human activity. The first suspect was fracking. Since the beginning of this century the oil and gas fields in Oklahoma, Kansas, Texas and elsewhere have seen a boom in this procedure, which helps improve the extraction of hydrocarbons from underground. Geologic formations are broken and cracked by injecting water under high pressure from the wellhead. Because such cracking of rocks is a process very similar to the generation of earthquakes in nature, it seemed plausible to blame the sudden increase in the seismicity rate on fracking. However, the temblors resulting from fracking are way too small to be felt by humans. Bill Ellsworth, a former seismologist at the USGS now at Stanford, summarized in the journal "Science" in 2013: "More than 100,000 wells have been subjected to fracking in recent years, and the largest induced earthquake was magnitude 3.6, which is too small to pose a serious risk."
The real culprit, it turned out, also had something to do with oil and gas production. Virtually every hydrocarbon field in the world contains a significant amount of water, which is pumped to the surface together with the oil. In the United States alone, about 21 billion barrels of this so called "produced water" are generated each year from about 900,000 wells. This is equivalent to a volume of 2.4 billion gallons per day. Because this produced water contains salts, remnants of the oil and many other organic and inorganic chemicals, it cannot be flushed into regular wastewater treatment plants or even released untreated into rivers or creeks. It is simply too hazardous. To dispose of this water, it is pumped back into the ground, usually in injection wells deep below the groundwater aquifers and the oil producing formations. There are more than half a million such injection wells in the US, most of them in Texas, California, Oklahoma and Kansas.
Figure 2: This hockey stick curve shows the enormous increase in seismicity for quakes with magnitudes 3 or larger in the mid-western states since 2009.
While the great majority of these wells are operated without any problems, some wells, particularly in Oklahoma, have become very problematic. These wells reach more than 7000 feet deep below the surface into the Arbuckle formation, a roughly 500 million year old layer of limestone. It lies right above the crystalline basement rocks. Once large amounts of waste water are pressed into the Arbuckle formation, the pore pressure in this formation as well as in the basement rocks increases. This in turn can activate earthquake faults deep in the basement, which have been dormant for millions of years. The hypocenters of most of the recent quakes in Oklahoma seem to lie on such slumbering, hitherto unknown faults.
Once seismologists established this cause and effect relationship, mid-western states started to change their regulations on operating wasterwater injection wells. Until recently, most regulations made sure that the wastewater did not come into contact with groundwater to avoid any contamination. This summer, however, the regulatory agencies in Oklahoma and Kansas have started to limit the daily volume of wastewater injection into those Arbuckle wells.
Although this order seems to have slowed down the earthquake activity somewhat, Saturday's temblor showed that the seismic hazard is not reduced. Hence, the Oklahoma Corporation Commission, the state's regulatory agency for the oil and gas industry, ordered a complete moratorium. Around 35 wells within an approximately 500-square-mile area around the epicenter of the quake will have to shut down their operation within the next seven to 10 days. (hra127)
As of this writing, the death toll of Wednesday's earthquake in Central Italy has risen to 280. However, rescue workers expect to find more bodies in the rubble in the three mountain communities most affected by the shaking of the magnitude 6.2 quake: Amatrice, Accumoli and Arquata del Tronto. Of particular worry is the situation in Amatrice, where a hotel has completely collapsed. Many tourists had spent the week there to attend the town's annual Pasta Festival. The celebrated specialty dish „Spaghetti all’amatriciana“ is well known all over Italy.
While rescue and recovery work is still continuing in the epicentral region, experts have begun to ask why relatively weak earthquakes always seem to generate enormous amounts of death and destruction in Italy. Compare, for instance, the Napa earthquake that occurred in Northern California almost exactly two years ago with Wednesday's temblor in the Italian Appenine mountains. With a magnitude of 6.0 the Napa quake was just a tad smaller than the magnitude 6.2 quake in Italy. But only one person was killed in California's wine country and the damage to buildings and structures was far less than the severe destruction in Italy. Elsewhere in the industrialized world even much stronger earthquakes with magnitudes of 7.5 or more do not generate as much damage as it seems to be the norm for smaller quakes in Italy.
|Rescue and recovery teams are still working in the town of Amatrice.|
Take the L'Aquilla event from 2009 with a magnitude of 6.3, only 25 miles from Wednesday's temblor: 300 people died and more than 10,000 buildings were destoyed. In 2002 more than 30 people, among them 27 pupils, died in a magnitude 5.9 quake south of the current epicenter. Other devastating Italian quakes also do not belong into the class of strong or severe earthquakes: One near Assisi in 1997 with a magnitude of 6.4 caused 11 fatalities, in a magnitude 6.4 quake south of Naples in 1997 more than 2700 people died and one thousand were killed in the Friuli quake of 1976 (M=6.5).
One reason for the enormous destruction caused by relatively small quakes in Italy can be traced to the age of many buildings, particularly in small, rural towns and villages. Many structures there date back centuries or even to the Middle Ages. When they were built, nobody cared or had a clue about earthquake resistant construction methods. However, earthquake engineers have also encountered modern buildings which did not comply with those aspects in the Italian building code, which relate to earthquake safety and resiliance. The 27 pupils mentioned earlier died in a modern school building in the town of San Giuliano di Puglia. It turned out that during its construction the earthquake safety measures required by law were bypassed or ignored.
|Built by modern standards: The red building in this picture is the only structure in the historic center of Armatrice left undamaged by Wednesday's quake. Photos: AP|
Another reason is that - in contrast to other industrialized countries located in seismic zones - Italy does not seem to have a culture of preparing for natural disasters. This sentiment was echoed after Wednesday's quake by Francesco Peduto, the president of Italy's National Council of Geologists. He said in a newspaper interview, that Italy was "lacking a culture of disaster prevention". He added that 40 percent of the 60 million Italians live in zones with a high natural hazard, mostly due to seismic activity but also in volcanic zones, like those around Vesuvius near Naples and Etna in Sicily. Even in areas with high seismic risk, there is little education of the general public on how to behave during earthquakes. While in Japanese and California schools kids are regularly taught to "Drop, Cover and Hold on" when they feel seismic shaking, very few Italian schools have any disaster drills. Peduto estimated that between 20 and 50 percent of all deaths in earthquakes could be avoided, if people knew how to react properly when shaking starts.
Another critic is Massimo Cocco, one of the research directors of the Italian National Institute for Geophysics and Volcanology (INGV). He estimates that almost 70 percent of Italy's buldings are built with little or no earthquake resistance. The Italian government, he claims, does not even have a "Earthquake Safe" plan for schools and hospitals. Peduto concurs and demands nationwide legislation to enforce earthquake retrofitting. Not only would such a measure reduce the loss of life, it would also save money in the long run. The national Association of Builders, an industry group, estimates that since 1968 Italy has spent about 200 billion Dollars in reconstruction and recovery efforts after earthquakes. Applying well tested retrofitting and building techniques to increase earthquake resistance would have cost a fraction of that amount, Peduto notes. (hra126)
The strong magnitude 6.2 earthquake that shook Central Italy around 3:30 this morning (local time) must have revived horrible memories for many people in the Rieti and Abbruzo regions about 100 miles north-northeast of Rome. Seven years ago, a temblor of similar size shook the same area and left the medieval town of L'Aquila in ruins. More than 300 people died in that quake, which has become one of the most infamous temblors in recent Italian history. First reports about today's quake in Italian media put the death toll at about 120. The reports speak of strong shaking and widespread damage.
Earthquakes in central Italy are a direct consequence of the complex collision of two tectonic plates. Although geographically a European country, Italy is actually a nail shaped protrusion of the African plate which rams into Europe, creating the Alps far north of this morning's epicenter. This collision has also created the Apennine Mountains. They run along the shaft of the "boot" which Italy resembles when viewed on a map. The Apennines are dominated by a series of north-south trending earthquake faults, which run parallel to the crest of the mountain range through most of central Italy. The epicenters of both the 2009 earthquake and today’s quake lie less than 25 miles apart on those fault lines. Today's quake occurred near the town of Amatrice to the north-northwest of L'Aquila.
|Map of the seismic risk in the Italian Apennines: areas in green and blue are considered very low risk. The pink in the center of the map has the highest risk. The white star denotes the location of today's quake. Source: INGV, Rome|
Besides the difference in the extent of damage and in the number of lives lost, there are several reasons why the two quakes are hard to compare. While today's quake was followed by several significant aftershocks - one of them reached a magnitude 5.5 - it was not preceded by any noticeable foreshocks. This was different in 2009. In the months before the April 6th quake, the area around L'Aquila was pummeled by hundreds of quakes. Although most of them were small, they were felt by the local population and rattled their nerves. As a consequence, Italy's government established a commission of experts, who were tasked with evaluating the seismic hazard in relation to this earthquake swarm, which seemed to go on and on.
While these experts were discussing various scenarios, an engineer without any prior knowledge of seismology stole the show. He had observed that the concentration of radon in some groundwater wells had changed during the swarm. Because he had read somewhere that such a change may be an indicator for an upcoming strong earthquake, he predicted in public that a strong quake was imminent. He did not discuss his findings with any seismologist. The commissioners reacted to this surprise announcement by trying to assure the population that such predictions were nonsense - only to be superseded by reality. A few days after the engineer went public, the devastating quake did indeed happen. Because their reaction was deemed completely inadequate, several commissioners were later found guilty of manslaughter.
Before today's quake, however, nobody had attempted a prediction and no commission was in session to gloss over the seismic risk along the fault lines in the Apennines. In fact, this region of Central Italy is considered to have one of the highest seismic risks in the nation.
One factor that certainly contributed to the widespread damage is the focal depth of today's quake. The seismologists at the Italian national seismic network computed a focal depth of only 2.5 miles. The closer a quake's origin is to the Earth's surface, the stronger the shaking and, hence, the more damage can be expected. (hra125)
California is full of faults. Although this sentence is a cheap pun amongst seismologists, it was the first thing that came into the blogger's mind when he heard about the surprising temblor in Lake County on Tuesday night (August 9th) around 8 pm. With a magnitude of 5.1, the quake was felt from Point Arena on the coast all the way east to Chico and Oroville in the Sierra foothills. It was located in a remote area of the southern Mendocino National Forest about 25 miles northeast of Ukiah and 10 miles south of Lake Pillsbury at a depth of 8 miles.
The epicenter of tuesday evening's quake (yellow star) was located on the southern section of the Bartlett Springs Fault. This fault is the eastern limit of the plate boundary. To the west are the Maacama and the San Andres Fault. (Modified after USGS)
It occurred along a fault that most Californians will have never heard of: the Bartlett Springs Fault. This faultline runs for about 100 miles through Lake County, from the Round Valley Indian Reservation in the North through the waters of Lake Pillsbury until it ends in the south, when it crosses Bartlett Springs Road east of Clear Lake. This road and the nearby spring gave the fault its name. Much of the fault runs through the new "Berryessa Snow Mountain National Monument," which President Obama created by proclamation about a year ago.
Even though the Bartlett Springs Fault was identified by geologists decades ago, it has hardly been investigated in detail. One reason for the lack of research activity is that rather few quakes happen along this fault when compared to the seismicity along other faults in Northern California like the San Andreas or Calaveras Faults. Tuesday's quake was the strongest temblor along this fault for more than 50 years. The other reason is that the population density along the Bartlett Springs fault is very low - keep in mind that all of Lake County has a population of less than 70,000 people. Both points together make the seismic risk, which is the potential for damage and losses due to an earthquake, along the Bartlett Springs Fault considerably lower than here in the Bay Area.
Nevertheless, as Tuesday's temblor showed, this fault is active. In addition, Jim Lienkaemper, the geologist with the US Geological Survey in Menlo Park who probably did more seismic investigations along the Bartlett Springs Fault than anybody else, found creep along some sections of the fault. He found that the two sides of the fault move past each other at a rate of about a quarter of an inch per year.
The Bartlett Springs Fault is part of the wide zone of earthquake faults generated by the boundary between the Pacific and the North American plates, which governs the geology of most of California. Although such boundaries are drawn on maps as single, narrow lines, they are in fact broad zones, which can be dozens of miles wide. Look at the Bay Area itself. Here the plate boundary is split into several faults, which run parallel to each other. The westernmost extension of this zone is the San Gregorio Fault, which lies mostly offshore. It is followed to the east by the San Andreas, the Hayward, the Calaveras, and finally the Greenville Fault, which is located east of Livermore. The distance between the San Gregorio Fault and the Greenville Fault is more than 50 miles - which is in fact the width of the plate boundary here in our area.
The situation is similar in Lake County up north. Coming from the east, the Bartlett Springs Fault is the first stepping stone from the North American to the Pacific Plate. It is followed in the west by the Maacama Fault, which essentially runs along Highway 101 between an area northeast of Santa Rosa and Laytonville. Finally, the western limit of the boundary zone is defined by the San Andreas Fault itself. The San Andreas Fault picks up about half of the movement between the plates, which is estimated to be about two inches per year. The Maacama Fault creeps by at about half an inch per year, and the Bartlett Fault moves, as mentioned above, by about a quarter inch. (hra124)