UPDATE: Potential Quake Hazard In Spokane Area - Spokane, North Idaho News & Weather KHQ.com

UPDATE: Potential Quake Hazard In Spokane Area

Posted: Updated:

Note: There will be a news conf. today at 10am. KHQ.com will stream it LIVE.

Mobile users, click this link to see LIVE stream: http://tinyurl.com/mkjes49

SPOKANE, Wash. - Preliminary interpretations of a recent geophysical survey confirm the presence of earthquake faults and reveal the possibility of previously unknown faults beneath the greater Spokane area.

During the spring of 2013, the U.S. Geological Survey undertook an airborne magnetic survey over the Spokane area to help understand the geologic reasons for a series of earthquakes and ground uplift that occurred several years earlier.

A sequence of 105 small (less than magnitude 4) earthquakes occurred beneath Spokane in 2001, accompanied by a small increase (1/2 inch) in ground elevation.  The shape of the deforming ground surface was consistent with movement on a northeast-trending fault beneath Spokane, yet no known mapped faults in Spokane have been active in the last 1.6 million years. 

To find the Spokane fault that caused 105 earthquakes in 2001, and evaluate its potential for large earthquakes in the future, scientists turned to geophysical tools to "see" below the surface. Knowing a fault's length, depth, and history of earthquakes helps us prepare for future earthquake hazards.

"As the director of Spokane Emergency Management, we work diligently on preparing our community for disasters which includes identifying hazards in our area. The USGS has performed studies and their preliminary findings will help us develop effective mitigation strategies," said Spokane County Sheriff Ozzie Knezovich.

"Geologic processes often bring together rocks with slightly different magnetic properties, and these variations cause very small differences in magnetic fields above the Earth's surface," explained the study's lead author, USGS geophysicist Richard Blakely. 

"In an aeromagnetic survey, a magnetic sensor is flown back and forth close to the ground and along closely spaced, parallel lines.  After data processing, we arrive at a map of ‘magnetic anomalies' reflecting the variations in the magnetic signal of the rocks and geology of the upper part of the Earth's crust."

Movement along a fault is an example of a geologic process that brings together different kinds of rocks. On a magnetic anomaly map, faults often appear as linear features, even though the faults themselves may be concealed below sedimentary deposits, vegetation, or urban development.

Several linear patterns are evident in the new Spokane data. Two prominent anomalies in the southeast corner of the survey extend across the entire area. One of these is caused by the Cheney fault zone; the other is probably caused by a similar, previously unrecognized zone of faults and fractures. The Latah Creek fault and other known faults appear in the new data as complex alignments of magnetic anomalies.

One alignment of magnetic anomalies is of particular interest: It crosses Spokane in a northeast direction, passes through the zone of earthquakes, and coincides with the Spokane fault postulated from ground deformation. 

There are many geologic reasons for linear magnetic anomalies, and the presence of unrecognized faults is just one possibility. Future USGS studies, including airborne LiDAR surveys and ground-based geologic investigations are planned to confirm the Spokane fault.

  • Most Popular StoriesMost Popular StoriesMore>>

  • NEW INFORMATION: High Drive brush fire believed to be human caused

    NEW INFORMATION: High Drive brush fire believed to be human caused

    Wednesday, July 30 2014 1:58 PM EDT2014-07-30 17:58:17 GMT
    SPOKANE, Wash.- Tuesday evening the Spokane Fire department announced they had a likely cause for the High Drive brush fire: humans. The fire broke out Monday afternoon about 3pm on the west side of Spokane's South Hill between Qualchan Golf Course and High Drive. By 6pm it had grown to 30 acres and moved to within 75 yards of several homes on High Drive.>>
    SPOKANE, Wash.- Tuesday evening the Spokane Fire department announced they had a likely cause for the High Drive brush fire: humans. The fire broke out Monday afternoon about 3pm on the west side of Spokane's South Hill between Qualchan Golf Course and High Drive. By 6pm it had grown to 30 acres and moved to within 75 yards of several homes on High Drive.>>
  • PHOTOS JUST IN: Devastation from Carlton Complex; 300 homes burned

    PHOTOS JUST IN: Devastation from Carlton Complex; 300 homes burned

    Saturday, July 26 2014 12:07 AM EDT2014-07-26 04:07:59 GMT
    TWISP, Wash. (AP) - The Okanogan County Sheriff says the Carlton Complex wildfire has many more homes than previously thought. Sheriff Frank Rogers said Friday that the Carlton Complex fire has consumed about 300 homes this month. His office previously placed the number at 150, but he said then he knew it would rise.>>
    TWISP, Wash. (AP) - The Okanogan County Sheriff says the Carlton Complex wildfire has many more homes than previously thought. Sheriff Frank Rogers said Friday that the Carlton Complex fire has consumed about 300 homes this month. His office previously placed the number at 150, but he said then he knew it would rise.>>
  • WILDFIRE WATCH 2014: DNR tackling new wildfire near Tonasket

    WILDFIRE WATCH 2014: DNR tackling new wildfire near Tonasket

    Wednesday, July 30 2014 3:03 PM EDT2014-07-30 19:03:06 GMT
    TONASKET, Wash.- The Department of Natural Resources says they are battling a new wildfire northeast of Wauconda and Tonasket. The fire broke out on Tuesday, July 29th and is called the "Torado Mountain" wildfire. DNR crews are attacking this fire from the ground and air.
    >>
    TONASKET, Wash.- The Department of Natural Resources says they are battling a new wildfire northeast of Wauconda and Tonasket. The fire broke out on Tuesday, July 29th and is called the "Torado Mountain" wildfire. DNR crews are attacking this fire from the ground and air.
    >>
  • Top Stories from KHQTop StoriesMore>>

  • Manhunt in Peone Prairie for man believed to be armed

    Manhunt in Peone Prairie for man believed to be armed

    Thursday, July 31 2014 3:01 AM EDT2014-07-31 07:01:36 GMT
    SPOKANE COUNTY, Wash.- At 6pm Wednesday evening two people arrived at their home, in Peone Prairie, and found two men in the process of ransacking it. This happened at a home near East Moffat and North Forker Road, northeast of Spokane.. >>Details on manhunt inside>>
    SPOKANE COUNTY, Wash.- At 6pm Wednesday evening two people arrived at their home, in Peone Prairie, and found two men in the process of ransacking it. This happened at a home near East Moffat and North Forker Road, northeast of Spokane. >>Details on manhunt inside
    >>
  • Green Bluff grass fire: 3 buildings destroyed at Walker's Farm

    Green Bluff grass fire: 3 buildings destroyed at Walker's Farm

    Thursday, July 31 2014 12:55 AM EDT2014-07-31 04:55:05 GMT
    GREEN BLUFF, Wash.- A fire that broke out Wednesday afternoon at a farm on Green Bluff was 100% contained by 6pm. The fire started on property owned by Walker's Farm. Fire crews were called out to the farm about 2:30pm.
    >>
    GREEN BLUFF, Wash.- A fire that broke out Wednesday afternoon at a farm on Green Bluff was 100% contained by 6pm. The fire started on property owned by Walker's Farm. Fire crews were called out to the farm about 2:30pm.

    >>
  • Q6 CARES: Air Conditioners and what you can do to help prevent them from breaking

    Q6 CARES: Air Conditioners and what you can do to help prevent them from breaking

    Wednesday, July 30 2014 11:01 PM EDT2014-07-31 03:01:06 GMT
    SPOKANE, Wash.- Before you crank up your air conditioner to its coolest setting, it's a good idea to make sure it's working properly. On Wednesday KHQ spoke with a maintenance tech, Justin Holyron, who works at RR Heating and Air Conditioning about some things you can check before calling in the experts. >>VIDEO INSIDE>>
    SPOKANE, Wash.- Before you crank up your air conditioner to its coolest setting, it's a good idea to make sure it's working properly. On Wednesday KHQ spoke with a maintenance tech, Justin Holyron, who works at RR Heating and Air Conditioning about some things you can check before calling in the experts. >>VIDEO INSIDE
    >>