The Comprehensive Test Ban Treaty Organization (CTBTO) held a conference in Vienna in 2009 that focused on progress made in monitoring the treaty. Six months earlier it had solicited contributions from scientists utilizing data that the organization had collected and analyzed. I made two presentations at the conference using seismic data I received in response to their solicitation.
Meredith Nettles of Lamont and I obtained data from 2000 through 2008 that the CTBTO’s monitoring arm had collected based on their seismic locations within 62 miles (100 km) of six sites used previously for nuclear testing. Identifying events at those sites is of great importance to policy makers. We found that all of those events could be identified as either earthquakes or explosions down to very low magnitudes in China, India, Pakistan, North Korea, and various other countries that are or may be capable of nuclear testing in the future.
Nettles and I examined thirty-eight seismic events of magnitude 3.3 and larger; the International Data Center of the CTBTO usually does not report events that are smaller than this. Most occurred near the former test sites of China, the United States, and Pakistan. No events were reported by the center near the Russian site at Novaya Zemlya or India’s test site, both very quiet locations for earthquakes. The identification of small seismic events on or near Novaya Zemlya is described in chapter 12 and is not repeated here. All of the events we studied at the Nevada Test Site (NTS) were earthquakes. We identified all of those in North Korea, including two nuclear explosions and one earthquake.
Identification at magnitude mb > 3.3 for five of the six test sites corresponds to a yield threshold of a small fraction of a kiloton if no serious attempts have been made to evade detection. The identification limit for Pakistan corresponds to about one kiloton, but it likely can be improved by examining high-frequency seismic waves, which our group has not done thus far.
CHINA’S TEST SITE AT LOP NOR
China conducted all of its nuclear explosions at its Lop Nor test site in the northwestern part of the country. Nettles and I found that the Lop Nor site had the greatest number of seismic events within 62 miles (100 km) of it, more than the other five test sites combined. Most of the seismic events that we studied near that site occurred at depths greater than 10 miles (16 km), clearly indicating they were earthquakes. High-frequency seismic waves also identify them and the remainder of the events as earthquakes (figure 14.1).
FIGURE 14.1
Measurements of high-frequency seismic waves for earthquakes and explosions near the Chinese test site at Lop Nor from 2000 to 2008. The log of the amplitude ratio of P to Lg seismic waves is shown on the vertical axis. Triangles denote earlier nuclear explosions at regional stations. Circles indicate earthquakes. Explosions have higher values on the vertical axis than earthquakes for frequencies of 4 and 8 Hz (cycles per second).
Source: Kim, Richards, and Sykes, 2009.
Although authors of several papers noted that the seismic event of March 13, 2003, of magnitude 4.3 to 4.7 was difficult to identify—that it was an anomalous or “problem” event—we found that it could be identified positively as an earthquake by five different methods. The smallest seismic event of magnitude 3.4 that we identified near Lop Nor would correspond to a well-coupled explosion with a yield of about 0.09 kilotons (90 tons). Work by others had indicated an identification capability that was even better, about magnitude 2.5, with a yield of 10 tons (0.01 kilotons).
MONITORING NUCLEAR TESTING BY NORTH KOREA
North Korea is one of the few countries that have not signed the Comprehensive Nuclear Test Ban Treaty (CTBT). It withdrew from the Nonproliferation Treaty in 2003. In 2005 North Korea declared that it possessed nuclear weapons, testing underground in 2006, 2009, 2013, and 2016 at Punggye-ri, a remote site in the northeastern part of the country. Five North Korean tests were well recorded and occurred very close to one another.
Although isolated, North Korea is a relatively small country and can be monitored readily by stations in South Korea, China, eastern Russia, Mongolia, and Japan. It consists largely of old rocks through which seismic waves are transmitted easily. Figure 14.2 shows the large numbers of stations of the International Monitoring Service that detected the North Korean nuclear explosion of 2013 with a yield of about 10 kilotons.
FIGURE 14.2
Seismic and infrasound stations of the International Monitoring System that detected the North Korean nuclear explosion of 2013.
Source: Comprehensive Test Ban Treaty Organization, 2013.
Kim and Richards calculated ratios of high-frequency seismic waves for events in North Korea, which are very similar to those shown for China in figure 14.1. Though not shown here, those ratios readily identify the five North Korean nuclear tests from 2006 to 2016 and a few rare, small earthquakes and chemical explosions. Seismograms of the North Korean tests are characterized by large P and a small Lg waves. Seismograms of small earthquakes exhibit the reverse: large Lg waves and relatively small P waves.
Well-coupled nuclear explosions in North Korea, like these five, can be detected and identified down to a few tens of tons—a small fraction of a kiloton. Stations in South Korea detected infrasound signals—low-frequency sound waves in the atmosphere—for the 2009 explosion. They also were detected in Japan and eastern Russia and South Korea in 2013. Bomb-produced noble gases were identified for the 2006 and 2013 explosions.
Monitoring a large underground explosion called the “chemical kiloton” at the Nevada Test Site in 1993 showed that two nonradioactive gases included in the explosive charge—sulfur hexafluoride and helium 3—could be detected in minute amounts along cracks and joints at the surface in the general vicinity of the shot point. Typically, they were detected at times of low atmospheric pressure and not at times of high pressure. Bomb-produced noble gases from an underground test are expected to behave similarly. Xenon isotopes were detected relatively late for the North Korean explosion of 2013, perhaps because leakage occurred many days later.
Some scientists have questioned whether the 2009 test by North Korea was, in fact, a large chemical explosion because radioactive gases were not detected in surrounding countries but were observed for the even smaller explosion of 2006. Huge chemical explosions detonated suddenly and of similar yield (several kilotons) and seismic magnitude to that of the 2009 test are exceedingly rare. Most are detonated sequentially over times as long as a second to break rock effectively and to reduce damage to nearby structures. In addition, transporting that much chemical explosives to the North Korean test site would have required huge numbers of trucks or train cars, which presumably would have been detected by satellite imagery. I doubt the 2009 test was anything other than a nuclear explosion.
North Korea announced all five tests ahead of time as nuclear and made no attempt to hide that fact, except possibly by detonating them at deeper than normal containment depths. They wanted other countries, particularly the United States, to know that they had nuclear devices. The main danger of North Korea’s possessing nuclear weapons is not that they might be used to attack the United States or its allies, because the United States undoubtedly would counter that massively. Instead, the real danger is that materials, plans for weapons, or nuclear weapons themselves could be sold or transferred either to other countries or to terrorists. Countering those threats deserves higher priorities.
INDIA’S NUCLEAR TESTS
The main reason India conducted a nuclear explosion first in 1974 and again in 1998 was fear not of Pakistan, but mainly of China, which captured territory from India during the Himalayan war of October 1962. China tested its first nuclear device in 1964 and its first multimegaton thermonuclear device in 1967.
The modern Pakistani station at Nilore provided near real time seismic data for the nearby Indian nuclear tests of May 11, 1998, to the IRIS seismological data center in the United States. The test site at Pokhran is located in northwestern India near the Pakistani border.
India and Pakistan, which have signed neither the CTBT nor the Noproliferation Treaty, do not send data to the International Monitoring Center. For India this likely stems from its not obtaining the language it wanted in the treaty in 1996, coupled with its unstated desire to test more sophisticated nuclear devices than the one it first detonated in 1974. The nationalist BJP party authorized the 1998 Indian tests when it came to power. Indian scientists later published high-quality seismograms for the Indian tests of May 11 and the Pakistani tests of 1998. Published reports indicate that the United States was caught off guard by the first Indian tests in 1998.
Routine transmission of data from seismograph stations in India would be very helpful in monitoring Pakistan, China, Iran, and other parts of southern Asia. Near real time transmission of data would have aided assessment of the very damaging giant earthquake and tsunami off Sumatra and the Andaman Islands in December 2004. The seismic array in Niger in central Africa is one of the best monitoring stations for explosions and earthquakes in southern Asia, including India and Pakistan.
The Indian prime minister said on May 11, 1998, that the yields of its tests earlier that day were as expected and that they consisted of fission, low-yield, and thermonuclear devices. He said they were contained and that no radioactivity was released into the atmosphere. This was followed six days later by a statement from Indian scientists that “there was no harmful radioactivity [my italics] from the contained nuclear tests.”
The three nearly simultaneous nuclear explosions by India on May 11, 1998, produced craters and damage that can be seen on unclassified satellite images as well as in photographs released by India. It is hard to believe that radioactive materials, especially noble gases, were not vented, because explosions shallow enough to produce craters often leak radioactive gases. India’s explosions at Pokhran in 1998 were within 2 miles (3 km) of the crater produced by its first nuclear test in 1974.
The magnitude of 5.3 determined from global data for the three simultaneous explosions on May 11, 1998, indicates a total yield of about 14 to 20 kilotons. The combined yield for the three tests as announced by the India’s Bhabha Atomic Research Centre, however, was considerably higher, 58 kilotons. It is hard to comprehend that the yield based on global data could have been underestimated by a factor of three to four. India’s official yield for the 1974 test, called the Smiling Buddha, was 20 kilotons, also higher than estimates made by other countries.
India obtained the plutonium for its 1974 explosion from a non-safeguarded reactor that followed a Canadian design. The United States provided the heavy water moderator for the reactor. India claimed the 1974 test was a peaceful nuclear explosion and that it did not violate the Limited Test Ban Treaty, which it had signed. Still at issue is whether India violated its peaceful use agreements with Canada and the United States.
Debate has raged in the media among Indian nuclear scientists about whether their country obtained a dependable thermonuclear (hydrogen) device through its tests in 1998. Its relatively small seismic magnitude indicates it may have failed to produce its full yield. Thermonuclear devices typically are triggered by fission explosions with yields of about 10 to 20 kilotons. Some Indian nuclear scientists, in fact, claim India needs to test a larger thermonuclear device to make sure they have an H-bomb capability. Others in India say they do not need such a test. India, which has not tested a nuclear weapon since 1998, might well have tested a boosted fission weapon at that time.
India and Pakistan each have aircraft that can carry nuclear weapons to the other. India has tested ballistic missiles that can reach China and, of course, Pakistan. Future nuclear explosions by either India or Pakistan could lead the other to test. China then might test as well.
The use of nuclear weapons by India, China, or Pakistan against one another represents a great nuclear threat today. Huge populations are at risk. Each continues to pursue more advanced delivery systems. Pakistan’s nuclear arsenal continues to grow. Of particular concern is that neither India nor Pakistan may have mechanisms on their nuclear weapons to insure against unauthorized use or unplanned nuclear detonation during an accident or fire.
India also claimed soon afterward that it tested two small experimental nuclear devices with yields of 0.2 and 0.6 kilotons nearly simultaneously two days later, on May 13, 1998, at 06 hour 51 minutes. I know of no seismic stations that recorded those claimed very small explosions. The Nilore Pakistani station had a signal-to-noise ratio of about 1000 for the combined explosions two days earlier on May 11. My colleague Paul Richards found that Nilore had the capability to detect a combined yield on May 13 of about 0.025 kilotons (25 tons). Those estimates of yield assume they were conducted in the same rock type as those on May 11. This is much smaller than the announced Indian combined yield of 800 tons. India described one of the tests on May 13 as having been detonated in a sand dune, a poor coupling material. If so, the combined yield could have been one to a few hundred tons, still smaller than the combined announced yields.
Possible explanations of these inconsistencies are: (1) the two events detonated but were much smaller than one to a few hundred tons; (2) either they both failed to detonate or only the one of 200 tons did; (3) the yields were poorly calibrated by India, as they were for the explosions of May 11; or (4) the yields were exaggerated.
The implications for monitoring are that if craters were formed today as claimed by India for the two very small explosions on May 13, 1998, they would be detectable by satellite imagery and synthetic aperture radar (INSAR). If radioactivity was released, such an event set off today should be detectable. In any case, if one or both of those explosions on May 13 occurred in a sand dune, as claimed by India, it would be difficult to hide because dry sand is not a good medium for hiding a sub-kiloton clandestine nuclear explosion at shallow depth.
PAKISTAN’S NUCLEAR PROGRAM AND TESTS
The loss of East Pakistan (now Bangladesh) in a civil war may have triggered a 1972 political decision in Pakistan to begin a secret nuclear weapons program. India’s 1974 nuclear explosion likely gave additional urgency to the program. Pakistan and India clashed several times after the partitioning of the two countries in 1947 when each gained independence from Britain. The two countries have fought over territory in Kashmir many times. Pakistan’s conventional forces being inferior to those of India, whose population is considerably greater than Pakistan’s, likely contributed as well to its quest for nuclear weapons.
Pakistan announced it conducted two series of nuclear explosions in late May 1998, soon after India tested on May 11. It said that the first set consisted of five explosions, which were detonated nearly simultaneously. Many people have speculated that Pakistan wanted to “up India’s claim” of five tests earlier in May. Pakistan’s two sets of explosions were well recorded internationally. The combined yield of the first set was about 10 kilotons, the second about 5 kilotons.
Pakistan gained uranium enrichment technology from many sources. It also obtained knowledge about nuclear weapons and missile technology from China. A. Q. Khan, widely regarded as the father of Pakistan’s nuclear program, learned about centrifuge enrichment when he worked at the Uranium Enrichment Corporation, URENCO, in the Netherlands. URENCO provides enriched uranium for many European nuclear power plants. Khan stated that Pakistan began uranium enrichment in 1978 and produced highly enriched uranium by 1983. He reportedly stated in an interview in a speech in January 2010 that Pakistan “had become a nuclear power” in 1984 or 1985.
In 1990 President George H. W. Bush failed to certify that Pakistan did not possess a nuclear explosive device. The United States hesitated on several occasions to declare that Pakistan had a nuclear weapons program because of its desire to obtain Pakistani help in combating the Russian invasion of Afghanistan and in pursuing a war against the Taliban and Al Qaeda.
Khan’s nuclear assistance extended to several countries was likely the most dangerous act of proliferation thus far during the nuclear age. The U.S. Congressional Research Service reported in May 2012 that Khan and his network had sold centrifuge technology for uranium enrichment to Libya in 1984. Libya revealed and gave up its nuclear facilities in December 2003. It then signed the CTBT and the Nonproliferation Treaty. One reason Libya did so was fear that the United States, Britain, and other countries would invade it. Materials that had clearly originated from Khan’s group in Pakistan were found in documents that Libya surrendered. Khan announced in 2005 that he and his associates had sold centrifuge technology to North Korea. They may have offered similar assistance to Iran, Egypt, and perhaps Syria and Saudi Arabia.
In their 2009 book The Nuclear Express, Thomas Reed and Danny Stillman say they believe Pakistan tested its first nuclear bomb in 1990 at China’s Lop Nor site. China considered Pakistan to be a regional ally. Others have expressed more uncertainty about the amount of Chinese nuclear assistance.
Reed was a former nuclear weapons designer at Livermore, secretary of the Air Force, and a special assistant to President Reagan for national security policy. Stillman worked at Los Alamos for decades in nuclear design, diagnostics, and testing. He directed the Los Alamos Technical Intelligence Division for thirteen years. They were experts on Soviet and Chinese nuclear weapons. Reed and Stillman also describe how various countries acquired nuclear expertise from others who already possessed nuclear weapons.
In an interview in U.S. News and World Report, Reed said, “There are numerous reasons why we believe this to be true, including the design of the weapon and information gathered from discussions with Chinese nuclear experts.” Reed claims that the Pakistanis were so quick to respond to the Indian nuclear tests in May 1998 because the Chinese had already helped them prepare for a test to be conducted within Pakistan. Reed also noted, “It only took them two weeks and three days [to respond and test].” Reed and Stillman claim the Pakistani test on May 28, 1998, likely was a single explosion, not five. It was of an advanced HEU (highly enriched uranium) design. It is clear from seismic data that Pakistan conducted tests at two separate sites in May 1998.
The United States was concerned several times about Pakistan’s ongoing production of nuclear weapons and its political instability that could lead to weapons’ falling into the hands of insurgents and perhaps terrorists. Pakistani officials and high military officers have stated many times, however, that their nuclear weapons are secure.
Nettles and I worked on the identification of seismic events located in the vicinity of the two Pakistani nuclear tests. Pakistan is second only to Lop Nor in the number of earthquakes per year within 62 miles (100 km) of their test sites. We obtained focal mechanism solutions of the very long period type for ten moderate-size seismic events from 1980 to 2008, which indicated that they were earthquakes, not explosions. We found that all but one of the Pakistani earthquakes occurred at depths of 12 to 44 miles (18 to 61 km), indicating that they must have been earthquakes. Several other seismic events in Pakistan were identified as earthquakes using the Ms-mb technique.
Identification of small earthquakes in Pakistan could be much improved by analyzing high-frequency seismic waves, which the Lamont group has not done. Seismic data from nearby stations in Afghanistan, Oman, and the United Arab Emirates have become available recently. Data from Indian and Iranian stations would be valuable as well to better monitor Pakistan. It is understandable that Pakistan did not make seismic data available for its tests later in May 1998. Monitoring, of course, needs to assume that a country testing a nuclear device will not provide seismic data from its own stations, at least not immediately.
ISRAEL’S NUCLEAR PROGRAM
Although none of the countries in the Middle East has declared that it possesses nuclear weapons, Israel maintains a policy of nuclear ambiguity. In the arms control community, it is very widely thought that Israel started to acquire nuclear weapons in the 1960s and now possesses about eighty. Its Dimona reactor, constructed with French help, went critical in December 1963, according to Reed and Stillman.
Israel, France, and Britain went to war with Egypt in October 1956 to reopen the Suez Canal, which had been seized by President Gamal Abdel Nasser. President Eisenhower publicly opposed the operation, and the Soviet Union issued an ultimatum to Britain, France, and Israel to desist, threatening actions that would menace the existence of Israel. Humiliated by the two superpowers, the three countries believed they could no longer count on American support.
Reed and Stillman say, “It is quite clear that France and Israel undertook a joint nuclear weapons program in the aftermath of Suez. That relationship, on a commercial basis, continued for decades.” The Dimona reactor in Israel, which produced plutonium, was very similar to the reactor at Marcoule, France. Reed and Stillman state, “Some wags have noted that on February 13, 1960, the two nations went nuclear with one test [in Algeria].” If true, this would explain why Israel has a modern nuclear arsenal without having tested by itself in the 1960s. Israel, a small country, does not have a test site of its own and is easily monitored from surrounding countries.
ISRAELI AND SOUTH AFRICAN NUCLEAR COOPERATION
Reed and Stillman claim, “After the Yom Kippur War of 1973, Israel and South Africa established closer nuclear ties, and Israel was assured of a uranium supply well into the future.” In 1997 South African officials announced that Israel had helped it develop nuclear weapons.
On September 22, 1979, a U.S. satellite detected a “double flash” typical of a small nuclear explosion over the southern oceans. U.S. hydrophones on Ascension Island in the equatorial Atlantic, designed to be used for listening for underwater sound, picked up signals that were consistent with a nuclear explosion in the Indian Ocean on or near South Africa’s Prince Edward Islands. Seymour Hersh, an American investigative journalist, stated in 1991 that a flotilla of South African and Israeli military ships had been tracked by the U.S. National Security Agency to a site near the Islands. Some media reports, apparently based only on the satellite data, placed the event incorrectly in the South Atlantic.
Many people in the U.S. weapons labs and the Defense Department concluded then, and continue to think, that it was a small nuclear explosion, perhaps of a neutron bomb that Israel thought it needed for close combat with tanks and Arab forces as occurred during the 1973 war. The double flash could not have occurred at a less opportune time for the Carter administration as the president was about to submit the second Strategic Arms Limitation Treaty (SALT II) to the Senate and to run for reelection on his success with nonproliferation. At the time, American foreign policy was in jeopardy in Iran following the overthrow of the shah and the capture of American hostages.
Carter convened a panel of scientists, including Lamont’s William Donn, to examine classified data related to a possible small nuclear explosion. Their mandate, however, was to examine only technical data. Hersh says, “Our capturing it [the double flash] fortuitously was an embarrassment, a big political problem, and there were a lot of people who wanted to obscure the event.” The panel, which was chaired by Jack Ruina of MIT, concluded that the flashes probably were not caused by a nuclear explosion but perhaps by a micro-meteorite hitting the satellite. Others attributed it to a small nuclear explosion close to the ground by Israel in cooperation with South Africa. Nevertheless, the global monitoring system is certainly capable of detecting and identifying such an event today. That is one reason the International Monitoring System includes more than just seismic monitoring.
Israel signed but has not ratified the Comprehensive Nuclear Test Ban Treaty (CTBT), nor has it signed the Nonproliferation Treaty. Israel does furnish data to the International Monitoring Center in Vienna, including information from a seismic array.
SOUTH AFRICAN NUCLEAR PROGRAM
South Africa developed first-generation nuclear weapons during the apartheid era. In the 1970s it became concerned about armed forces that opposed its regime in the former Portuguese colonies of Angola and Mozambique, in Southern Rhodesia (now Zimbabwe), and in South-West Africa (now Namibia). South Africa was further distressed by the introduction of Cuban troops into Angola and by warfare in South-West Africa. These forces, as well as embargoes against it, led South Africa to pursue a nuclear weapons program.
Soviet satellites detected South Africa’s development of a nuclear test site in the Kalahari Desert in July 1977. They and the United States put pressure on South Africa not to test a crude, first-generation uranium weapon, which it did not do.
Late in 1993 President F. W. de Klerk disclosed details about South Africa’s abandoning its nuclear weapons program in 1989 and dismantling six gun-type uranium 235 nuclear weapons, similar to the one dropped on Hiroshima in 1945. In is unknown whether those crude weapons would have worked, but many people assumed that they would. The government of de Klerk did not want those weapons to fall into the hands of a new government under Nelson Mandela. The International Atomic Energy Agency declared that the South African shafts in the Kalahari Desert had not been used for nuclear testing and, in 1993, that they had been rendered useless for nuclear tests.
South Africa is the only country that has destroyed its inventory of nuclear weapons. Sweden actively planned to acquire nuclear weapons in 1945 but then halted those programs in 1968. On June 1, 1996, Ukraine became “nuclear free” after returning the last of its 1900 Soviet-era strategic nuclear weapons to the Russian Federation. All three countries went on to sign and ratify the Nonproliferation Treaty and the CTBT.
MONITORING THE NEVADA TEST SITE
Nettles and I also studied seismic events from 1992 to 2008 within 62 miles (100 km) of the Nevada Test Site (NTS). Focal mechanism solutions of the very long period type, measurements of Ms-mb, and data on high-frequency waves at regional stations indicate that all seismic events near NTS of magnitude greater than 3.3 could be identified as earthquakes. Unlike earthquakes near the Chinese and Pakistani test sites, shocks on and near NTS are quite shallow and hard to identify using just the seismic waves pP and sP (figure 3.1). Nevertheless, the three other methods sufficed for positive identification of them as earthquakes even though NTS is a region characterized by poor propagation of seismic P waves.
IRAN AND THE MIDDLE EAST
The 2012 National Academies report The Comprehensive Nuclear Test Ban Treaty examined the monitoring of the CTBT for Iran and other parts of the Middle East. Understandably, those countries are of major concern to many in terms of their possibly acquiring and testing nuclear weapons. Iran signed but has not ratified the CTBT. About a decade ago, it allowed the International Monitoring Service (IMS) to operate seismic stations on its territory. After the IMS certified them, however, data were no longer transmitted abroad even though the stations still exist.
Major concern about Iranian nuclear intentions led me to devote particular attention recently to the geology and earthquakes of Iran. If Iran acquires nuclear weapons, Egypt, Saudi Arabia, Turkey, and some Gulf states may also decide to do so. Iran still has some centrifuges running that produce enriched uranium, claiming it enriches materials solely for the generation of nuclear power. Its reactors and the amounts of enriched uranium are subject to the agreement reached in 2015 by Iran, the five main nuclear powers, Germany, and the European Union.
Since earthquakes occur often in Iran, distinguishing their seismic signals from those of underground nuclear explosions is of concern to many nations. Hence, I now describe the tectonic settings of Iranian earthquakes pertinent to their identification.
Iran is largely a region of continental convergence caught between the Arabian and Eurasian plates. Similar deformation extends into northeastern Iraq, the Caucasus, eastern Turkey, and Turkmenistan. Compression causes the continental crust of Iran to be squeezed outward into its surrounding countries and the southern Caspian Sea. In contrast, the oceanic plate beneath the Arabian Sea is being subducted along the Makran plate boundary of southeastern Iran and southern Pakistan. Subduction is inhibited today elsewhere in Iran.
The Arabian plate underthrusts the southwestern side of the Zagros Mountains along the Persian Gulf in southwestern Iran and northeastern Iraq. The crystalline rocks of the crust beneath the Zagros are part of the Arabian plate. Oceanic crust was subducted along the northeastern side of the Zagros about 80 million years ago. The suture zone and the Main Reverse Fault that remain from that former subduction are largely devoid of earthquakes. A second period of crustal shortening occurred in the Zagros during the last few million years. GPS measurements indicate that active crustal shortening is concentrated along the frontal, southwestern part of the Zagros belt.
Iran has a long history of damaging and deadly earthquakes. In 1997 M. Berberian stated that earthquakes had killed 126,000 Iranians during the previous hundred years. In their 1982 book A History of Persian Earthquakes, N. N. Ambraseys and C. P. Melville list many shocks and the destruction of cities going back thousands of years. The Tabas earthquake (magnitude Mw 7.4) of September 1978 in east-central Iran and the Rudbar-Tarom earthquake (magnitude Mw 7.7) of June 1990 in northwestern Iran were the most catastrophic earthquakes in Iran during the twentieth century, killing more than 20,000 and 40,000 people, respectively. Financial losses from the June 1990 earthquake were about $7.2 billion, about 10 percent of Iran’s gross national product. About 30,000 deaths occurred in the moderate-size Bam earthquake of December 2003 (magnitude 6.6) in southeastern Iran. Poor construction and the shallow depths of those earthquakes contributed to the large loss of life and high damage.
Large earthquakes (figure 14.3) do not occur randomly throughout Iran but are concentrated in the Alborz Mountains in the north, in northwestern Iran, along faults surrounding the otherwise nearly nonseismic Lut block between 27 and 34 degrees north and 57.5 to 60 degrees east in eastern Iran, and in the Kopet Dag Mountains along Iran’s northeastern border with Turkmenistan. Since 1918 most of the earthquakes along the Zagros Mountains have not exceeded magnitude 6.5, but many shocks of small to moderate size have occurred there. Central Iran, which is located between these zones of higher activity, has few large or moderate-size earthquakes.
FIGURE 14.3
Locations and magnitudes of large earthquakes (Mw>5.4) in Iran and surrounding regions from 1900 to 2009.
Source: R. Engdahl, personal communication, 2013.
Other large earthquakes have occurred in adjacent countries. The largest, of magnitude 8, occurred in 1945 off the coast of Pakistan, not Iran, along the Makran subduction zone (figure 14.3). Uplifted terraces along the coast in the Iranian part of Makran are indicative of past great shocks.
Monitoring possible nuclear testing by Iran involves the identification of seismic signals of possible explosions as distinct from those of the many moderate-to-small earthquakes that occur every year. Accurate determination of depths is key to identifying many seismic events as earthquakes.
In 2004 M. Tatar and colleagues obtained the most accurate depths of seismic events in the Zagros Mountains using local portable stations. The earthquakes they studied occurred within the upper 5 to 10 miles (8 to 16 km) of the crust; none were deeper than 20 miles (32 km). They report that these earthquakes are likely located in the upper part of crystalline crust below the very thick sedimentary layers of the Zagros. The thick Hormuz salt, which is about 430 to 600 million years old, is found at the base of those sediments and the top of the crystalline basement.
This is fortunate for verification because most of the earthquakes they examined beneath the Zagros were much deeper than any nuclear explosions that could be detonated there. Hence, accurate determinations of depths using data from local seismic stations are exceedingly valuable for the identification of events as either explosions or earthquakes.
Many sources of data on Iran’s earthquakes and geology are accessible to those interested in seismic verification. The great loss of life and destruction from past shocks led the Iranian government many decades ago to work on reducing earthquake losses through the operation of seismic networks, engineering of buildings to better withstand strong shaking, geologic studies, and mapping of active faults. Many papers on these topics, as well as on Iran’s petroleum resources and their geology, have been published over the past century.
In 2009 Michael Pasyanos and colleagues made an extensive study of thousands of paths that seismic waves travel from earthquakes in the Middle East to tens of regional seismic stations. They also used data from stations and earthquakes within Iran. In 2013 Mark Fisk of Alliant Techsystems and Scott Phillips of the Los Alamos Lab studied hundred of thousands of paths traversed by four different types of seismic waves in Asia, Europe, and the Middle East. The two studies show in detail how well or how poorly seismic waves are detected at various frequencies for many seismic paths and how well events can be identified as being either explosions or earthquakes. Both studies provide a rationale for choosing data from seismic stations best suited to examining and identifying future seismic events.
IRAQ
The United States invaded Iraq in 2003. Government claims that Iraq possessed an active program to develop nuclear weapons turned out to be false. Another false accusation was that Iraq had obtained uranium from Niger in central Africa. France, however, gets uranium from Niger, a former colony, and carefully controls Niger’s export. The United States is said to have destroyed Iraq’s uranium (yellow cake) earlier, during the first Gulf War. Another false claim was that Iraq had conducted one or more decoupled nuclear explosions beneath a large lake in 1989. Iraq subsequently signed and ratified the CTBT.
DEALING WITH PROBLEM SEISMIC EVENTS GLOBALLY: A SUMMARY
The numbers and sizes of various problem or anomalous seismic events decreased dramatically from 1960 to mid-2009 (figures 14.4 and 14.5). It should be remembered that these are a tiny fraction of the earthquakes and chemical explosions that are reported every year. Most problem seismic events are small, occurring near the lower end of seismic detectability at the time.
FIGURE 14.4
Unidentified nuclear explosions, alleged explosions, unidentified seismic events, and identified nuclear explosions by India, Pakistan, and North Korea from 1997 to mid-2009. Seismic magnitude is at the left side and yield in kilotons (kt) at the right. Downward-pointing arrows indicate that events were equal in size or smaller.
FIGURE 14.5
Events not identified and problem (anomalous) seismic events identified as earthquakes through special studies: Eastern Kazakhstan, E Kaz; Kara Sea, Kara; Kola Peninsula, Kola; Nevada Test Site, NTS; Novaya Zemlya, NZ. CCD 72 are seismic events from a U.S. document tabled in 1972 at the UN’s Conference of the Committee on Disarmament.
Source: Sykes and Nettles, unpublished poster, 2009.
Figure 14.4 shows unidentified nuclear explosions, alleged nuclear explosions, and seismic events that were not positively identified initially, as well as recorded nuclear explosions by India, Pakistan, and North Korea from 1970 to mid-2009. Nuclear explosions that were not identified soon after they occurred are denoted by solid triangles. They decreased in size from about 8 kilotons in 1965 to about 0.3 kilotons in 1985. We found no unidentified nuclear explosions or any unidentified events larger than magnitude 2.5 (or 0.005 kilotons, 5 tons, if they were nuclear) after 1989.
Solid squares indicate nuclear explosions by India, Pakistan, and North Korea. They are the only countries that tested after the Comprehensive Nuclear Test Ban Treaty was open for signature in September 1996. The three did not sign the treaty. India and Pakistan last tested in 1998.
Seismic waves were not found, despite diligent searches, for one alleged nuclear explosion on September 19, 1989, in Iraq. That claim, which was publicized by dissidents, is almost certainly false. The seismic event in North Korea on May 22, 1989, which concerned some people in the United States, could not be identified at the time. There is no indication, however, that North Korea tested as early as 1989. Seismic waves were not detected for two suspect Russian tests on September 8 and 23, 1999, at Novaya Zemlya, as reported by Bill Gertz in the Washington Times. Noise measurements indicate that those events were not larger than magnitude 2.0 and 2.5. Both may have been permitted subcritical tests—that is, ones with no release of nuclear energy.
Figure 14.5 shows problem or “anomalous” seismic events that were later identified as earthquakes through special studies. Their magnitudes decreased from 5.6 in the mid-1960s to 2.7 by 2009. If they had been nuclear explosions, which they were not, their detectability in terms of yield improved over time from about 30 kilotons to 0.003 kilotons (3 tons). Nettles and I identified the problem event of 2003 near China’s Lop Nor test site as an earthquake by five different techniques.
Nettles and I also identified (not shown) several large mine collapses in various countries of magnitude 2.8 to 5. They are typically richer in long-period seismic waves than earthquakes, making their identification as distinct from underground nuclear explosions even easier. Mechanism solutions for some of those events also indicate that they were collapses and not explosions. Several very large chemical explosions were detected and identified as well.
In summary, the detection and identification of problem seismic events of several kinds—earthquakes, nuclear explosions, alleged nuclear explosions, mine collapses, and chemical explosions—have improved dramatically over the past five decades. A residuum of less than one problem event per year in countries of concern to the United States can be reduced further with special studies.
