Categorized | Earthquake, News

Light 4.2M quake strikes Southwest of Lanai, no tsunami threat

Magnitude 4.2 Earthquake Southwest of Moloka`i

By USGS/HVO

The U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) recorded a magnitude-4.2 earthquake located southwest of the Island of Moloka‘i on Friday, August 22, 2014, at 2:37 a.m., HST. The Pacific Tsunami Warning Center has determined that no damaging tsunami was generated (http://ptwc.weather.gov/?region=2).

The earthquake was located 55 km (34 mi) west-southwest of Maunaloa, Moloka‘i. A map showing the location of the earthquake is posted on the HVO website at http://hvo.wr.usgs.gov/seismic/volcweb/earthquakes/.

The depth of the earthquake was calculated to be shallow—about 6 km (4 mi). However, determining accurate earthquake locations and depths in this region can be difficult because of the sparse coverage of seismometers on Moloka‘i and adjacent islands. Earthquake locations are most accurate when seismometers surround the earthquake source, which is nearly impossible given the geography of the islands in the area. Often, the depths are the most uncertain in these situations. Therefore, subsequent and more sophisticated analysis will likely result in locating this earthquake at a greater depth in the mantle.

HVO’s seismic records show that 3 earthquakes of magnitude 3 or larger have occurred in the same area in the past 25 years.

According to Wes Thelen, HVO’s Seismic Network Manager, earthquakes outside of the Island of Hawai`i are not uncommon and are typically caused by a structural adjustment of the mantle in response to the weight of the Hawaiian Islands. “This event is a good reminder that the Island of HawaiÊ»i is not the only Hawaiian island prone to earthquakes,” he said.

Earthquake activity generally decreases northwest up the Hawaiian Island chain, but the potential for larger earthquakes still exists. Earthquakes with magnitudes greater than 6.0 occurred in the Moloka‘i region in 1870, 1871, 1895 and 1894.

“No aftershocks have been recorded, and aftershocks typically do not follow earthquakes at these depths in the mantle,” Thelen added.

Today’s earthquake was felt on several Hawaiian islands, from the Island of Hawai‘i to O‘ahu. The USGS “Did you feel it?” Web site (http://earthquake.usgs.gov/eqcenter/dyfi/) received more than 70 felt reports by 8:00 a.m., HST, ranging from weak to light shaking. Thus far, there have been no reports of damage, nor do we expect any given the location and size of the earthquake.

“The earthquake today caused no detectable changes on the active volcanoes on the Island of Hawai‘i,” said Jim Kauahikaua, HVO’s Scientist-in-Charge.

The magnitude was initially estimated at 4.0, but more detailed seismic analyses resulted in a final magnitude of 4.2.

The 2nd annual Great Hawai`i Shakeout, scheduled for 10:16 a.m. on October 16, 2014, is an opportunity for all Hawaii residents to practice “Drop! Cover! Hold On!”—actions that are proven to reduce injury in an earthquake. For details, please visit shakeout.org/hawaii/.

For information on recent earthquakes in Hawaiʻi and eruption updates, visit the Hawaiian Volcano Observatory website at hvo.wr.usgs.gov.

The USGS provides science for a changing world. For more information, visit www.usgs.gov.
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View M4.2 – 61km S of Waimanalo Beach, Hawaii – 2014-08-22 12:37:17 UTC in a larger map

Magnitude
4.2

Event Time
2014-08-22 12:37:17 UTC
2014-08-22 01:37:17 UTC-11:00 at epicenter
2014-08-22 02:37:17 UTC-10:00 HST

Location
20.794°N 157.590°W depth=6.2km (3.9mi)

Nearby Cities
61km (38mi) S of Waimanalo Beach, Hawaii
63km (39mi) SSE of Honolulu, Hawaii
69km (43mi) SSE of Kailua, Hawaii
72km (45mi) SSE of Kane’ohe, Hawaii
72km (45mi) SE of ‘Ewa Beach, Hawaii

TSUNAMI SEISMIC INFORMATION STATEMENT NUMBER   1
NWS PACIFIC TSUNAMI WARNING CENTER EWA BEACH HI
258 AM HST FRI AUG 22 2014

TO - CIVIL DEFENSE IN THE STATE OF HAWAII

SUBJECT - LOCAL TSUNAMI INFORMATION STATEMENT

THIS STATEMENT IS FOR INFORMATION ONLY. NO ACTION REQUIRED.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

   ORIGIN TIME - 0237 AM HST 22 AUG 2014
   COORDINATES - 20.6 NORTH  157.6 WEST
   LOCATION    - IN THE DEEP OCEAN SOUTHWEST OF LANAI
   MAGNITUDE   - 4.1

EVALUATION

 NO TSUNAMI IS EXPECTED. REPEAT. NO TSUNAMI IS EXPECTED.
 HOWEVER...SOME AREAS MAY HAVE EXPERIENCED SHAKING.

THIS WILL BE THE ONLY STATEMENT ISSUED FOR THIS EVENT UNLESS
ADDITIONAL DATA ARE RECEIVED.

USGS: How large does an earthquake have to be to cause a tsunami?

Magnitudes below 6.5
Earthquakes of this magnitude are very unlikely to trigger a tsunami.

Magnitudes between 6.5 and 7.5
Earthquakes of this size do not usually produce destructive tsunamis. However, small sea level changes may be observed in the vicinity of the epicenter. Tsunamis capable of producing damage or casualties are rare in this magnitude range but have occurred due to secondary effects such as landslides or submarine slumps.

Magnitudes between 7.6 and 7.8
Earthquakes of this size may produce destructive tsunamis especially near the epicenter; at greater distances small sea level changes may be observed. Tsunamis capable of producing damage at great distances are rare in the magnitude range.

Magnitude 7.9 and greater
Destructive local tsunamis are possible near the epicenter, and significant sea level changes and damage may occur in a broader region.

Note that with a magnitude 9.0 earthquake, the probability of an aftershock with a magnitude exceeding 7.5 is not negligible. To date, the largest aftershock recorded has been magnitude 7.1 that did not produce a damaging tsunami.

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