Aftershocks likely from September test detected from North Korea nuclear site: USGS

WASHINGTON (Reuters) - Two minor tremors were detected on Saturday from near North Korea's nuclear test site and were probably aftershocks from the country's massive nuclear test in early September, a U.S. Geological Survey official said.

The aftershocks, of magnitude 2.9 and 2.4, were detected at 0613 and 0640 GMT (1:13 a.m. and 1:40 a.m. EST) respectively, said the USGS and Lassina Zerbo, executive secretary of the Vienna-based Comprehensive Nuclear-Test-Ban Treaty Organization.

A tweet from Zerbo said analysts had confirmed that the activity was "tectonic" in origin.

The USGS official said the tremors had been in the vicinity of the Punggye-ri nuclear test site, where North Korea conducted its sixth and largest underground nuclear test on Sept. 3.

SEE ALSO: Nobel Peace Prize winners warn the world is 'one tantrum away' from nuclear crisis

"They're probably relaxation events from the sixth nuclear test," the official said. "When you have a large nuclear test, it moves the earth's crust around the area, and it takes a while for it to fully subside. We've had a few of them since the sixth nuclear test."

Pyongyang said the September test was of an H-bomb, and experts have estimated it was 10 times more powerful than the U.S. atomic bomb dropped on Hiroshima in 1945.

A series of quakes since then has prompted experts and observers to suspect the test might have damaged the mountainous location of its site in the northwest tip of North Korea, where all of the country's nuclear tests have been conducted.

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Kim Jong Un watches launch of Hwansong-15 missile in North Korea
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Kim Jong Un watches launch of Hwansong-15 missile in North Korea
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows North Korean leader Kim Jong-Un looking at launching of the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
North Korea's leader Kim Jong Un is seen as the newly developed intercontinental ballistic rocket Hwasong-15� test was successfully launched, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang November 30, 2017. REUTERS/KCNA ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. REUTERS IS UNABLE TO INDEPENDENTLY VERIFY THIS IMAGE. SOUTH KOREA OUT. NO THIRD PARTY SALES. NOT FOR USE BY REUTERS THIRD PARTY DISTRIBUTORS
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows launching of the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows launching of the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows launching of the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows launching of the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows North Korean leader Kim Jong-Un looking at launching of the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows North Korean leader Kim Jong-Un looking at launching of the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency (KCNA) shows North Korean leader Kim Jong-Un looking at launching of the Hwansong-15 missile which is capable of reaching all parts of the US. THIS PICTURE WAS MADE AVAILABLE BY A THIRD PARTY. AFP CAN NOT INDEPENDENTLY VERIFY THE AUTHENTICITY, LOCATION, DATE AND CONTENT OF THIS IMAGE. THIS PHOTO IS DISTRIBUTED EXACTLY AS RECEIVED BY AFP. / AFP PHOTO / KCNA via KNS AND AFP PHOTO / KCNA VIA KNS / South Korea OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / KCNA VIA KNS / BYLINE' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read KCNA VIA KNS/AFP/Getty Images)
A view of the newly developed intercontinental ballistic rocket Hwasong-15� test that was successfully launched, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang November 30, 2017. REUTERS/KCNA ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. REUTERS IS UNABLE TO INDEPENDENTLY VERIFY THIS IMAGE. SOUTH KOREA OUT. NO THIRD PARTY SALES. NOT FOR USE BY REUTERS THIRD PARTY DISTRIBUTORS
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South Korea's spy agency told South Korean lawmakers in October that North Korea might be readying two more tunnels at the site.

North Korea hinted its next nuclear test could be above ground after U.S. President Donald Trump warned in September that the United States would "totally destroy" North Korea if it threatened America.

Another possible obstacle to North Korea's use of Punggye-ri for tests is the nearby active volcano of Mount Paektu, which North Koreans consider a sacred site. Its last eruption was in 1903, and experts have debated whether nuclear testing could trigger another.

SEE ALSO: Japan, US, South Korea to hold missile tracking drill amid North Korea crisis

North Korea's official media reported on Saturday that national leader Kim Jong Un had scaled Mount Paektu with senior military officials to "emphasize his military vision" after completion of the country's nuclear force.

Kim declared the nuclear force complete after the test of North Korea's largest ever intercontinental ballistic missile last month, which experts said puts all of America within range.

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How to survive a nuclear attack
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How to survive a nuclear attack

What should you do in the event of a nearby nuclear attack? Click through to learn more. 

(Photo by Lambert/Getty Images)

Seek shelter immediately, towards the center of a building or -- preferably -- a basement. Aim for the same type of shelter you would utilize in the event of a tornado. 

(Photo via Getty Images)

The next three slides are examples of nuclear shelters that exist around the world. 

(Image via Lawrence Livermore National Laboratory)

The entrance of Shelter Co.'s nuclear shelter model room, which is placed in the basement of the company's CEO Seiichiro Nishimoto's house, is pictured in Osaka, Japan April 26, 2017. (Photo via REUTERS/Kim Kyung-Hoon)
A fallout shelter sign hangs on the Mount Rona Baptist Church, on August 9, 2017 in Washington, DC. In the early 60's Washington was at the center of civil defense preparations in case of a nuclear blast, with over one thousand dedicated public fallout shelters in schools, churches and government buildings. (Photo by Mark Wilson/Getty Images)
A 'shelter' sign is displayed at the entrance to a subway station in Seoul on July 6, 2017 in Seoul, South Korea. According to the metropolitan government, South Korea's city subway stations serve a dual purpose with over 3,300 designated as shelters in case of aerial bombardment including any threat from North Korea. The U.S. said that it will use military force if needed to stop North Korea's nuclear missile program after North Korea fired an intercontinental ballistic missile on Tuesday into Japanese waters. The latest launch have drawn strong criticism from the U.S. as experts believe the ICBM has the range to reach the U.S. states of Alaska and Hawaii and perhaps the U.S. Pacific Northwest. (Photo by Chung Sung-Jun/Getty Images)

Dense materials, including dirt or thick walls, provide the best defense to fallout radiation.

(Photo via Getty Images)

If possible, take a warm shower -- but do not use conditioner, as it can bond to nuclear particles. 

(Photo via Getty Images)

Do not seek shelter in a car, as they won't provide adequate protection, and you should not attempt to outrun nuclear fallout. 

(Photo by Noel Hendrickson via Getty Images)

The nuclear fallout zone shrinks quickly after an attack, but the less dangerous "hot zone" still grows. 

(Image via Lawrence Livermore National Laboratory)

Once you are sheltered, do not leave. Listen to a radio or other announcements. 

(Photo via Getty Images)

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(Reporting by David Brunnstrom; Editing by Lisa Von Ahn)

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