Earth-shaking events in Amboseli

Wed, 2007-07-18 05:14 by hcroze · Forum/category:
Location of earthquake Time of day of 15 tremors between 12-18 July 07

The Amboseli elephant research team felt the earth shaking late afternoon on the 17th of July. Just after 5 PM local time the nearly 6-magnitude tremor started. The team ran out of the office and their quarters for safety. The shock lasted nearly a minute. One of the nearby Ol Tukai Lodge cottages was on fire, and the team spent the next hour helping lodge staff to quell the blaze. No one was hurt.

This is the latest in a series of small earthquakes that has been rocking Kenya and Tanzania over the past few days. It's getting rather close to home: the US Geological Survey Earthquake Hazards Program tells us the epicenter was some 90 km (55 mi) dues west of the Elephant Research Headquarters in the middle of Amboseli National Park.

The image shown here comes from the USGS website at the location given below. We've added the annotations: Red Arrow, the epicenter; (1) AERP Elephant Research Headquarters; (2) Oldonyo Lengai, said to be the last active volcano in East Africa; (3) Lake Natron. The Kenya-Tanzania border is the diagonal grey line.

Here's the official USGS story to date:

"The sequence of earthquakes that has been occurring in northern Tanzania since July 14, 2007, represents a seismic phenomenon known as a seismic "swarm"-- an episode of high earthquake activity in which the largest earthquake does not occur at the beginning of the episode and in which the largest earthquake is not substantially larger than other earthquakes of the episode. Worldwide, earthquake swarm activity is commonly associated with tectonic regions in which both strike-slip fault and normal faulting occur and where magmatic activity occurs at shallow depths in the earth's crust.

"The earthquake swarm is situated close to the Ol Doinyo Lengai volcano, an active volcano in the Gregory Rift of the East African rift system. Although volcanic eruptions are often preceded and accompanied by earthquake swarms, most earthquake swarms are not associated with volcanic eruptions. Information recorded at the U. S. Geological Survey/National Earthquake Information Center is not sufficient to determine if the current Tanzania swarm activity reflects a geologic process that might lead to a change in the eruptive behavior of Ol Doinyo Lengai.

"The East African rift system is a diffuse zone of crustal extension that passes through eastern Africa from Djibouti and Eritrea on the north to Malawi and Mozambique on the south and that constitutes the boundary between the Africa plate on the west and the Somalia plate on the east. At the earthquake's latitude, the Africa and Somalia plates are spreading apart at a rate of several millimeters per year. The largest earthquake to have occurred in the rift system since 1900 had a magnitude of about 7.6. Earthquakes within the East African rift system occur as the result of both normal faulting and strike-slip faulting." (http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007exbe.php#su...)

Image source: http://maps.google.com/maps?q=-2.5828+36.2829(M6.0%20-%20TANZANIA%20-%202007%20July%2017%20%2014:10:43%20UTC)&ll=-2.5828,36.2829&spn=2,2&f=d&t=h&hl=e

More tremors

Wed, 2007-07-25 07:10 by hcroze

The 'swarm' continued till the 19th of July. Here is the USGS list updated as of 25-Jul, all in Tanzania (from http://earthquake.usgs.gov/eqcenter/recenteqsww/Maps/10/35_-5_eqs.php):

MAG UTC DATE-TIME LAT LON DEPTH km
4.0 2007/07/19 21:07:19 -2.661 35.940 10.0
4.5 2007/07/19 02:14:11 -2.675 36.023 10.0
4.9 2007/07/18 17:25:52 -2.776 36.129 10.0
4.8 2007/07/18 10:29:16 -2.676 35.983 10.0
4.5 2007/07/18 08:48:25 -2.982 36.312 10.0

Have heard rumours that there is an ash plume coming from Oldonyo Lengai, but have not seen or heard any sound evidence. Might just have to go have a look.
_________
HC

Tremors

Wed, 2007-07-18 22:41 by Jan

I understand from the newspapers that the aftershocks were 6.1 on the Richter scale. Those are pretty strong tremors!!

What I am interested in knowing, what was the reaction of the wildlife in Amboseli? Did you see the elephants acting differently. Were any of them nervous or stampeding?

I vaguely remember that after one of the tsunamis several years ago elephants ran for the hills before anything happened, so they must have sensed what was about to happen in their feet long before the people knew it. Please let us know of any intersting wildlife events during the tremors.

I know Kilimanjaro has been dormant for many years. Is there any possibility that a quake close to Kili could awaken it?

Sleeping Kili?

Thu, 2007-07-19 08:18 by hcroze

As I recall from Celia Nyamweru's book, Rifts and Volcanoes, Kili is dormant rather than extinct. Same is true of Longonot. She says (p. 74), "They still have well-formed craters and show signs of underground heat in the escape of steam and other gases." I guess the implication is that something sleeping can be awakened.

Concerning animal reactions in Amboseli, no reports as yet. We'd have to be lucky to be with an ele group at the very moment of a tremor. But there is a chance. According to the USGS (http://earthquake.usgs.gov/eqcenter/recenteqsww/Maps/10/35_-5_eqs.php), between 12 July and yesterday (the 18th) there have been 15 little quakes in the area, 7 during the day (0600-1800) and 8 at night (1800-0600). They ranged between 4.2 and 5.9 magnitude (despite up to 6.1 being reported in the media). I've added a graph above showing the distribution of tremor times throughout 24 hours. Looks like being in the field all afternoon and into the evening would be a good bet to observe a reaction.

_________
HC

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