20.06
Raden Rahmad
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#10,380
After a 4 day break, the Saudi MOH is reporting two more MERS cases from Riyadh. One of the cases is listed as a contact of confirmed case, while the other case is still under investigation.
19.11Raden RahmadNo comments
#10,379
Since the H7N9 virus emerged in Mainland China in the spring of 2013, sparking the first of three mini-epidemics, 13 cases have turned up in Hong Kong. All are considered imported cases, as all had recent travel to the mainland, and no secondary infections among their contacts have been reported.
Ten of these cases were imported during the 2013-14 winter season, and today we’ve got a detailed epidemiological report on them from researchers at Hong Kong’s Centre for Health Protection.
The full text of the report is available (online or in PDF format), and is well worth reading it its entirety, as it sheds additional light on the demographics, symptomology, incubation period, duration of viral shedding, and effects of antiviral treatment with H7N9 cases.
First a brief excerpt from the abstract with appears in the Journal of Microbiology, Immunology and Infection (JMII), after which I’ll return with a bit more regarding one of their conclusions.
Epidemiology of human influenza A(H7N9) infection in Hong Kong
Yiu-hong Leung, May-kei To, Tsz-sum Lam , Shui-wah Yau, Oi-shan Leung, Shuk-kwan Chuang
Centre for Health Protection, Department of Health, Hong Kong, China
Published Online: July 25, 2015
DOI: http://dx.doi.org/10.1016/j.jmii.2015.06.004Abstract
Results
A total of 10 cases were reported and all were imported infection from Mainland China. Four patients died and the cause of death was related to influenza A(H7N9) infection in two patients. The median interval from illness onset to initiation of oseltamivir treatment for the severe cases (4.5 days) was significantly longer than the mild cases (2 days; p = 0.025). Severe cases had a significantly longer viral shedding duration than mild cases (p = 0.028). The median incubation period for cases with a single known exposure date was 4 days. Nasopharyngeal aspirate taken from the 88 close contacts of the 10 patients all tested negative for influenza A virus using reverse transcription polymerase chain reaction.
Conclusion
Delayed administration of antiviral treatment may be associated with a more severe illness for influenza A(H7N9) infection. Despite our aggressive contact tracing policy with laboratory testing of all close contacts, no secondary case was identified which implied that the potential of human-to-human transmission of the circulating influenza A(H7N9) virus remains low.
Although based on a limited number of cases (n=10), this study adds a bit more to the growing body of evidence that the early administration of antivirals can help reduce morbidity and mortality in cases of severe influenza.
While that won’t come as much of a surprise to most medical experts, given demonization that antivirals have received online and in the `popular press’ over the past few years, it is worth highlighting.
Much of the ire surrounding these drugs has been due to Roche’s long-standing resistance to releasing all of their testing data, and that has led to critical editorials in the BMJ, and frequent excoriation in the British press (see Daily Mail: Ministers blew £650MILLION on useless anti-flu drugs)..
As a result of this sort of hyperbolic coverage, many people have come away with the erroneous impression that these drugs are worthless – or worse.
While its benefits may be limited in mild influenza in healthy adults, we’ve seen numerous observational studies that show antivirals are useful in the treatment of severe flu (see Study: Antivirals Saved Lives Of Pregnant Women and Study: The Benefits Of Antiviral Therapy During the 2009 Pandemic), particularly in those with heightened risk factors.
And even more impressively (and perhaps, more importantly with avian flu viruses on the rise again), in 2010’s Study: Antiviral Therapy For H5N1, a study of outcomes of H5N1 patients who either received, or did not receive, antiviral treatment found:
Out of 308 cases studied, the overall survival rate was a dismal 43.5%. But . . . of those who received at least one dose of Tamiflu . . . 60% survived . . . as opposed to only 24% who received no antivirals.
Evidence which helps explain why, we’ve seen a push back by many public health agencies (see The CDC Responds To The Cochrane Tamiflu Study & UK PHE’s Revisiting Influenza Antiviral Recommendations), strongly recommending the early administration of antivirals in cases of severe flu or in patients with elevated risk factors.
While far from perfect, and not a `cure’ for flu, antivirals remain our best pharmaceutical option for the treatment of severe influenza.
19.42Raden RahmadNo comments
Flu Virus binding to Receptor Cells – Credit CDC
#10,378
Although ubiquitous in birds, until a couple of years ago, avian H6 viruses as human health threats were essentially flying under the radar. While implicated in the creation of H5N1 (see Hatta & Kawaoka, 2002), its history suggested that it posed little or no direct threat to human health – and after the return of H5N1 in 2003 – relatively little attention was paid to it
All that changed in May of 2013 when Taiwan health officials – employing heightened surveillance due to the outbreak of H7N9 on the Chinese mainland – stumbled across the first known human infection with an avian H6 virus (see Taiwan CDC Reports Human Infection With Avian H6N1)
The patient was described as a 20-year-old female who presented at local hospital with mild pneumonia on May 8th, was hospitalized and treated with oseltamivir, and who was released 3 days later. None of 36 close contacts followed up on were found to be infected with the H6N1 virus.
Six months later, in Taiwan CDC: Epidemiological Analysis Of Human H6N1 Infection, researchers warned that a (emphasis mine) “unique clade of H6N1 viruses with a G228S substitution of haemagglutinin have circulated persistently in poultry in Taiwan. These viruses continue to evolve and accumulate changes, increasing the potential risk of human-to-human transmission.”
Since then, we’ve seen a growing body of research emerge suggesting that H6 viruses in general – and H6N1 in particular – are possibly evolving towards a more human-adapted virus, and are therefore worthy of both our increased attention and surveillance.
Before avian influenza viruses can pose a serious threat to human health they must acquire a number of mammalian adaptations. Some we know about – like binding to human receptor cells and replicating at the lower temperatures found in mammalian airways – and others we don’t.
Arguably the most important step: the virus must be able to attach to the surface of cells in the respiratory tract, and in humans, that means binding to α2-6 receptor cells that are abundant in the upper airway (trachea).
Since avian flu viruses bind preferentially to the alpha 2,3 receptor cells found in the gastrointestinal tract of birds, a series of amino acid changes are needed in its RBS (Receptor Binding Site) to allow it to attach to human receptor cells. Some avian viruses can bind to both types of cells, although α2-6 binding is usually much weaker.
In the studies mentioned above there is growing evidence that the pendulum of binding preference in H6N1 may be swinging from avian to human receptors. Today, we’ve another study that adds weight to those concerns.
It’s a lengthy and highly technical report, and I would invite those so inclined to read it in its entirety at the link below. I’ve only excerpted the abstract.
The bottom line, however, is they found that the Taiwan H6 HA has a slight preference for human receptors, and that it may represent an intermediate step towards a complete human adaptation.
Research Article
Structural and Functional Studies of Influenza Virus A/H6 Hemagglutinin
Fengyun Ni, Elena Kondrashkina, Qinghua Wang
Published: July 30, 2015
DOI: 10.1371/journal.pone.0134576
Abstract
In June 2013, the first human infection by avian influenza A(H6N1) virus was reported in Taiwan. This incident raised the concern for possible human epidemics and pandemics from H6 viruses. In this study, we performed structural and functional investigation on the hemagglutinin (HA) proteins of the human-infecting A/Taiwan/2/2013(H6N1) (TW H6) virus and an avian A/chicken/Guangdong/S1311/2010(H6N6) (GD H6) virus that transmitted efficiently in guinea pigs.
Our results revealed that in the presence of HA1 Q226, the triad of HA1 S137, E190 and G228 in GD H6 HA allows the binding to both avian- and human-like receptors with a slight preference for avian receptors. Its conservation among the majority of H6 HAs provides an explanation for the broader host range of this subtype. Furthermore, the triad of N137, V190 and S228 in TW H6 HA may alleviate the requirement for a hydrophobic residue at HA1 226 of H2 and H3 HAs when binding to human-like receptors.
Consequently, TW H6 HA has a slight preference for human receptors, thus may represent an intermediate towards a complete human adaptation. Importantly, the triad observed in TW H6 HA is detected in 74% H6 viruses isolated from Taiwan in the past 14 years, suggesting an elevated threat of H6 viruses from this region to human health. The novel roles of the triad at HA1 137, 190 and 228 of H6 HA in binding to receptors revealed here may also be used by other HA subtypes to achieve human adaptation, which needs to be further tested in laboratory and closely monitored in field surveillance,
The finding that 74% of the H6N1 samples isolated from Taiwan over the past 14 years now carry this N137/V190/S228 triad, which allows the binding to both avian- and human-like receptors, suggests that these H6 viruses may represent a growing threat to human health.
While there is no clear winner in the avian flu sweepstakes, the field continues to broaden with each passing year. Where once we worried only about H5N1, over the past two years we’ve seen serious human infections with H7N9, H6N1, H5N6, and H10N8.
While the odds of any one of these subtypes becoming a `humanized’ flu strain are likely pretty long, the more candidates you have, the greater the chances are that one will succeed.
So we watch the evolutionary progress of viruses like H6N1 closely, in hopes that we’ll have some advance warning if it becomes a more tangible threat.
21.18Raden RahmadNo comments
#10,377
Last week’s FluView report on 1 Novel (H3N2v) Flu Case Reported In Minnesota marked the 375th known swine variant flu infection of a human over the past decade in the United States. As surveillance and testing is very limited, this number likely represents a small fraction of actual infections (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012).
During the 2012 outbreak, associated with attendance of state and county fairs in the Midwest, more than 300 cases were detected. Most were mild, and none of these viruses maintained transmission in the community (see EID Journal: H3N2v Swine To Human Transmission At Agricultural Fairs – 2012).
Although it hasn’t happened often - in 2009, we saw a swine-origin H1N1 virus, after kicking around in swine herds for a decade – adapt well enough to human physiology to spark the first pandemic in more than 40 years. While not a particularly severe pandemic, this event showed that pigs can generate a pandemic virus as well as birds.
While avian flu viruses are of great concern – particularly because of the observed high mortality rates in humans when infected with certain H5 and H7 strains – most of them fall between the H4 to H16 subtypes – none of which are known to have sparked a pandemic in the past.
There are some who wonder whether a non-H1, H2, or H3 virus has the `right stuff’ to spark a pandemic (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?).
Going back 125 years, only H1, H2 & H3 subtypes have sparked major epidemics, subtypes that typically circulate most often in humans and pigs (there are H1, H2, & H3 avian viruses as well).
125 Years of Pandemics – Credit ECDC
While this doesn’t preclude an H5 or an H7 avian virus from adapting enough to spark a pandemic, it is generally thought that novel or variant H1, H2 and H3 viruses have less of an evolutionary `leap’ to make. Which puts pigs high on our suspect when it comes to novel flu strains.
![Reassortant pig[6]](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhH3Fref-rRIvwFs0TUJhE0aNbcHs1hq_auF2UahYWjADFIJdmVWI2DyaVheneaX6rfWF4sBgGydmpQN_92eg-QjzDptfCJ0T-n3Ja1KfGkHuTuZVGHpQzFpzJOa2CO5yVLX23zlByDhvK9/?imgmax=800 "Reassortant pig[6]")
Since pigs can be infected by more than one flu virus at the same time, it is also possible for two viruses to swap genetic material (reassort), resulting in a new hybrid strain.
Here in North America we’ve been watching the evolution of several swine variant viruses (H1N1v, H1N2v, H3N2v) over the past few years, all of which have reassorted with - and picked up the M gene segment from – the 2009 H1N1 virus (see Keeping Our Eyes On The Prize Pig).
Not only are pigs excellent hosts and `mixing vessels’ for influenza, they tend to have a fair amount of contact with humans; on the farm, at county and state fairs, and at live markets. Places where humans can either pass their flu viruses onto pigs (reverse zoonosis), or catch swine variant viruses and potentially carry them into the community.
Hence the development of this year;s CDC Interim Guidance for Workers who are Employed at Commercial Swine Farms: Preventing the Spread of Influenza A Viruses and last year’s Measures to Minimize Influenza Transmission at Swine Exhibitions, 2014[189 KB, 6 pages].
All of which serves as prelude to a study, appearing this week in Clinical Infectious Diseases, that looks at the risks of swine variant flu transmission at live markets in the state of Minnesota. First a link, and some excerpts from the abstract, then a look at CIDRAP’s report on this last night.
Mary J. Choi1,*, Montserrat Torremorell2,*, Jeff B. Bender2, Kirk Smith3, David Boxrud3, Jon R. Ertl2, My Yang2, Kamol Suwannakarn2, Duachi Her3, Jennifer Nguyen3, Timothy M. Uyeki1, Min Levine1, Stephen Lindstrom1, Jacqueline M. Katz1, Michael Jhung1, Sara Vetter3, Karen K. Wong1, Srinand Sreevatsan2, and Ruth Lynfield3
Abstract
(EXCERPT)
Results. Nasal swabs from 11 (65%) of 17 employees tested positive for IAVs by rRT-PCR; seven employees tested positive on multiple occasions and one employee reported influenza-like illness. Eleven (73%) of 15 employees had baseline hemagglutination-inhibition antibody titers ≥40 to swine-origin IAVs, but only one demonstrated a 4-fold titer increase to both swine-origin, and pandemic A/Mexico/4108/2009 IAVs. IAVs were isolated from swine (72/84), air (30/45) and pen railings (5/21). Whole genome sequencing of 122 IAVs isolated from swine and environmental specimens revealed multiple strains and subtype codetections. Multiple gene segment exchanges among and within subtypes were observed, resulting in new genetic constellations and reassortant viruses. Genetic sequence similarities of 99%–100% among IAVs of one market customer and swine indicated interspecies transmission.
Conclusions. At markets where swine and persons are in close contact, swine-origin IAVs are prevalent and potentially provide conditions for novel IAV emergence.
This summary from CIDRAP’s News scan.
Flu viruses found in workers, animals at fairs
(EXCERPT)
Researchers from the CDC and Minnesota obtained samples from two markets that were epidemiologically linked to people with infections of variant swine-origin flu. Nasal swabs from 11 of 17 employees (65%) tested positive for influenza A, and 7 tested positive multiple times. Also, 11 of 15 workers (73%) had baseline hemagglutination-inhibition antibody titers of 40 or higher to swine-origin flu, and 1 had a fourfold titer increase to both swine-origin and 2009 H1N1 flu.
In addition, influenza A viruses were isolated from 72 of 84 swine (86%), from 30 of 45 air samples (67%), and from 5 of 21 railings (24%). Whole-genome sequencing of viruses isolated from swine and environmental specimens revealed multiple strains and subtype co-detections, with multiple gene segment exchanges.
Finally, genetic sequencing of viruses from a market customer and from swine indicated pig-to-human transmission or vice versa. The authors conclude that live-animal markets may provide conditions for novel flu viruses to emerge.
We’ve been fortunate that since the end of 2012 we’ve seen fewer human swine variant infections reported. Swine viruses continue to circulate and evolve (see last year’s USDA IAV-S Surveillance Program Detects Novel H3N1 In US Swine), however, and so the threat has not gone away.
19.43Raden RahmadNo comments
Credit WHO
#10,376
Fresh off of its 12:00 GMT embargo, we have an article appearing in The Lancet detailing the results of a a Phase III clinical trial of the rVSV-ZEBOV candidate Ebola vaccine - and while preliminary - the results are very encouraging.
Utilizing a `ring vaccination’ strategy – where relatives and neighbors of known Ebola cases are vaccinated to halt further transmission - early results suggest a high rate of protection.
Of the contacts who were vaccinated immediately after a case emerged– none developed the disease after more than 10 days post vaccination. While of contacts who received a delayed vaccination 3 weeks after the first case was detected, 16 fell ill.
We’ve some excerpts from the abstract and a link to a full report in The Lancet, followed by a press release from the World Health Organization.
Ana Maria Henao-Restrepo, Ira M Longini, Matthias Egger, Natalie E Dean, W John Edmunds, Anton Camacho, Miles W Carroll, Moussa Doumbia, Bertrand Draguez, Sophie Duraffour, Godwin Enwere, Rebecca Grais, Stephan Gunther, Stefanie Hossmann, Mandy Kader Kondé, Souleymane Kone, Eeva Kuisma, Myron M Levine, Sema Mandal, Gunnstein Norheim, Ximena Riveros, Aboubacar Soumah, Sven Trelle, Andrea S Vicari, Conall H Watson, Sakoba Kéïta, Marie Paule Kieny*, John-Arne Røttingen*
ABSTACT
Findings Between April 1, 2015, and July 20, 2015, 90 clusters, with a total population of 7651 people were included in the planned interim analysis. 48 of these clusters (4123 people) were randomly assigned to immediate vaccination with rVSV-ZEBOV, and 42 clusters (3528 people) were randomly assigned to delayed vaccination with rVSV-ZEBOV.
In the immediate vaccination group, there were no cases of Ebola virus disease with symptom onset at least 10 days after randomisation, whereas in the delayed vaccination group there were 16 cases of Ebola virus disease from seven clusters, showing a vaccine efficacy of 100% (95% CI 74·7–100·0; p=0·0036). No new cases of Ebola virus disease were diagnosed in vaccinees from the immediate or delayed groups from 6 days post-vaccination.
At the cluster level, with the inclusion of all eligible adults, vaccine effectiveness was 75·1% (95% CI –7·1 to 94·2; p=0·1791), and 76·3% (95% CI –15·5 to 95·1; p=0·3351) with the inclusion of everyone (eligible or not eligible for vaccination). 43 serious adverse events were reported; one serious adverse event was judged to be causally related to vaccination (a febrile episode in a vaccinated participant, which resolved without sequelae). Assessment of serious adverse events is ongoing.
Interpretation The results of this interim analysis indicate that rVSV-ZEBOV might be highly efficacious and safe in preventing Ebola virus disease, and is most likely effective at the population level when delivered during an Ebola virus disease outbreak via a ring vaccination strategy.
News Release WHO/ 37
31 July 2015World on the Verge of an Effective Ebola Vaccine
Geneva, 31 July 2015 – Results from an interim analysis of the Guinea Phase III efficacy vaccine trial show that VSV-EBOV (Merck, Sharp & Dohme) is highly effective against Ebola. The independent body of international experts - the Data and Safety Monitoring Board – that conducted the review, advised that the trial should continue. Preliminary results from analyses of these interim data are published today in the British journal The Lancet.
“This is an extremely promising development,” said Dr Margaret Chan, Director-General of the World Health Organization. “The credit goes to the Guinean Government, the people living in the communities and our partners in this project. An effective vaccine will be another very important tool for both current and future Ebola outbreaks.”
While the vaccine up to now shows 100% efficacy in individuals, more conclusive evidence is needed on its capacity to protect populations through what is called “herd immunity”. To that end, the Guinean national regulatory authority and ethics review committee have approved continuation of the trial.
“This is Guinea’s gift to West Africa and the world,” said Dr. Sakoba Keita, Guinea’s national coordinator for the Ebola response. “The thousands of volunteers from Conakry and other areas of Lower Guinea, but also the many Guinean doctors, data managers and community mobilisers have contributed to finding a line of defence against a terrible disease.”
“The “ring” vaccination method adopted for the vaccine trial is based on the smallpox eradication strategy,” said John-Arne Røttingen, Director of the Division of Infectious Disease Control at the Norwegian Institute of Public Health and Chair of the Study Steering Group. “The premise is that by vaccinating all people who have come into contact with an infected person you create a protective “ring” and stop the virus from spreading further. This strategy has helped us to follow the dispersed epidemic in Guinea, and will provide a way to continue this as a public health intervention in trial mode.”
The Guinea vaccination trial began in affected communities on 23 March 2015 to evaluate the efficacy, effectiveness and safety of a single dose of the vaccine VSV-EBOV by using a ring vaccination strategy. To date, over 4 000 close contacts of almost 100 Ebola patients, including family members, neighbours, and co-workers, have voluntarily participated in the trial.
The trial stopped randomisation on 26 July to allow for all people at risk to receive the vaccine immediately, and to minimize the time necessary to gather more conclusive evidence needed for eventual licensure of the product. Until now, 50% of the rings were vaccinated three weeks after the identification of an infected patient to provide a term of comparison with rings that were vaccinated immediately. This now stops. In addition, the trial will now include 13 to 17-year-old and possibly 6 to 12-year-old children on the basis of new evidence of the vaccine’s safety.
“In parallel with the ring vaccination we are also conducting a trial of the same vaccine on frontline workers,” said Bertrand Draguez, Medical Director at Médecins sans Frontières. “These people have worked tirelessly and put their lives at risk every day to take care of sick people. If the vaccine is effective, then we are already protecting them from the virus. With such high efficacy, all affected countries should immediately start and multiply ring vaccinations to break chains of transmission and vaccinate all frontline workers to protect them. ”
The trial is being implemented by the Guinean authorities, WHO, Médecins sans Frontières (MSF) and the Norwegian Institute of Public Health, with support from a broad partnership of international and national organizations.
“This is a remarkable result which shows the power of equitable international partnerships and flexibility,” said Jeremy Farrar, Director of the Wellcome Trust, one of the funders of the trial. “This partnership also shows that such critical work is possible in the midst of a terrible epidemic. It should change how the world responds to such emerging infectious disease threats. We, and all our partners, remain fully committed to giving the world a safe and effective vaccine. ”
“This record-breaking work marks a turning point in the history of health R&D,” said Assistant Director-General Marie-Paule Kieny, who leads the Ebola Research and Development effort at WHO. “We now know that the urgency of saving lives can accelerate R&D. We will harness this positive experience to develop a global R&D preparedness framework so that if another major disease outbreak ever happens again, for any disease, the world can act quickly and efficiently to develop and use medical tools and prevent a large-scale tragedy.”
18.28Raden RahmadNo comments
Seismic Hazard Map – Credit USGS
#10,375
In 2011 – during the bicentennial of the four great New Madrid earthquakes of 1811-12 – FEMA and other federal agencies mounted the largest National Level Exercise (NLE) to that date, revolving around a catastrophic earthquake occurring in the New Madrid Seismic Zone (NMSZ) that would involve eight Central U.S. States: Alabama, Arkansas, Kentucky, Illinois, Indiana, Mississippi, Missouri, and Tennessee spread across 4 FEMA regions (IV, V, VI, and VII).
While sparsely populated 200 years ago during the last big seismic event, a similar quake today would endanger millions of people living in the central United States, and likely cause severe economic and social disruption across an even wider area of the nation.
This National Level Exercise tested initial incident response along with disaster recovery plans. According to FEMA’s NLE fact sheet, the exercise was designed to validate the following capabilities:
While large quakes in the middle of the country are rare, the USGS, in Earthquake Hazard in the New Madrid Seismic Zone Remains a Concern, warns:
Continuing Preparedness Needed
The geologic record of repeated large earthquakes, the historical accounts of the 1811–12 large earthquakes, and the continuing earthquake activity in the area are compelling evidence that the New Madrid region has high earthquake hazard. The preponderance of evidence leads us to conclude that earthquakes can be expected in the future as frequently and as severely as in the past 4,500 years. Such high hazard requires prudent measures such as adequate building codes to protect public safety and ensure the social and economic resilience of the region to future earthquakes.
Complicating matters, earthquakes in the central and eastern part of the nation are generally felt over a much wider area than those on the west coast, due to differences in their underlying bedrock. In 2012’s USGS: Eastern Earthquakes - Rare But Powerful, we looked at this phenomenon.
The following shake map from the USGS shows the areas reporting shaking from two recent quakes, a 6.0 in Central California, and the recent 5.8 Virginia quake. By an incredibly large margin, the smaller eastern quake was felt over a much bigger area.
All of which serves as prelude to yesterday’s release from the USGS that shows that computer simulations indicate a future New Madrid quake could produce major, prolonged ground shaking in metropolitan areas across several states, including Memphis, TN, Paducah, KY, Evansville, IN, and Little Rock, AR.
Released: 7/30/2015 2:00:00 PM
Computer simulations of earthquake shaking, replicating the quakes that occurred in 1811-1812 in the New Madrid seismic zone (NMSZ), indicate that future large earthquakes there would produce major, prolonged ground shaking. The 1811-1812 events were some of the largest in the United States since its settlement by Europeans, and the NMSZ spans portions of seven states: Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee and Mississippi.
Scientists from the Universidad Nacional Autónoma de México, the U.S. Geological Survey, San Diego State University, AECOM (formerly URS Corporation), and the University of Memphis simulated a set of 20 hypothetical, yet plausible earthquakes located along two currently active faults in the NMSZ. The hypothetical earthquake scenarios range in magnitude from 7.0 to 7.7, and consider various possible epicenters.
”Based on our simulations, were the 1811-1812 earthquakes to repeat today, more than 8 million people living and working near the New Madrid seismic zone would experience potentially damaging ground shaking at modified Mercalli intensities ranging from VI to VIII,” said Leonardo Ramirez-Guzman, lead author of the paper that appears in the July 30 edition of the Bulletin of the Seismological Society of America.
“Strong ground shaking in the greater Memphis metropolitan area could last from 30 seconds to more than 60 seconds, depending on the magnitude and epicenter of a potential seismic event,” said Ramirez-Guzman, a professor at Universidad Nacional Autónoma de México and former USGS contract scientist.
The simulations also demonstrate the importance of fault rupture directivity (seismic energy focused along the direction of faulting), especially when combined with the wave channeling effects of the Reelfoot rift, a buried, northeast-southwest trending geologic valley in the NMSZ. In particular, future large earthquakes on the approximately 80-mile long NMSZ fault show strong shaking at vibration frequencies that pose a risk for mid-rise to high-rise buildings and tall bridges. This fault is thought to be responsible for the December 16, 1811 magnitude 7-7.7 earthquake. Some of the earthquake simulations showed strong shaking focused to the northeast as far as 100-200 miles away near Paducah, Kentucky and Evansville, Indiana, and to the southwest 150 miles toward Little Rock, Arkansas. An example of this earthquake shaking focusing effect can be seen here.
While it’s not possible to know which direction a fault will rupture once an earthquake starts, knowing that there is an increased chance of strong shaking along these geologically-defined corridors is a valuable aid in better characterizing seismic hazard and minimizing earthquake risk.
Earthquakes pose a significant risk to nearly 150 million Americans. The USGS and its partners in the multi-agency National Earthquake Hazard Reduction Program are working to improve earthquake monitoring and reporting capabilities via the USGS Advanced National Seismic System (ANSS). More information about ANSS can be found on the ANSS website.
Peak ground-motion variability for a magnitude 7.7 earthquake. Warmer colors indicate stronger ground motions. The stronger ground motions are extended further northeast and southwest caused by the channeling effect of the Reelfoot rift (RFR) The fault is displayed as a thick black continuous straight line, with the epicenter indicated by the triangle. (high resolution image 1.3 MB)
From my 10 years of living in the mostly rural Bootheel of Missouri, I know that most local residents are aware of the seismic history of the region, and are – in general – a fairly resilient lot. As farmers and ranchers, they tend to be a bit more self sufficient than those who live in surrounding cities.
But as mentioned above, a rupture of the New Madrid fault could have serious effects on cities 100-200 miles away.
Areas where millions of people live and work in structures that were not designed with earthquake safety in mind, and where severe disruptions of essential services (water, power, EMS) – particularly during the winter – could make life extremely difficult.
All of which makes participating in this year’s Great Central U.S. Shakeout, and preparing your home and family for an earthquake, all the more important. Those who live in other seismically active regions (worldwide) will want to visit Shakeout.org for information on your region’s activities.
For more recent blogs on earthquakes, and earthquake preparedness, you may wish to revisit:
OSU: Pragmatic Action - Not Fatalism - In Order To Survive The `Big One’
Shakeout.Org Twitter Chat On Earthquake Preparedness
USGS/OGS Joint Statement On Increased Earthquake Threat To Oklahoma
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