Earthquake Information – Haiti & Wisconsin

***Watch WISN 12 News Today at 5, 6, & 10pm for the latest weather updates!***

I’ve just added a story that ran on 12 News at Five from Meteorologist Sally Severson going into greater detail about the science behind the earthquake. Take a look.

Mark

Meteorologist Sally Severson talked with UW-Milwaukee’s Geo-sciences department today and they help explain why being on the fault line is a very precarious position.

Thank you for stopping by the Weather Watch 12 blog!  Not only do we focus on weather in this blog, but from time to time we will touch on the big science related story of the day.  Today we will look at science behind the earthquake that struck Haiti on Tuesday, and also look back at past Wisconsin quakes which were felt right here in Milwaukee!

All of us know what an earthquake is, but how does it occur.  Here is a brief description from the U.S. Geologic Survey:

An earthquake is the vibration, sometimes violent, of the Earth’s surface that follows a release of energy in the Earth’s crust. This energy can be generated by a sudden dislocation of segments of the crust, by a volcanic eruption, or event by manmade explosions. Most destructive quakes, however, are caused by dislocations of the crust. The crust may first bend and then, when the stress exceeds the strength of the rocks, break and “snap” to a new position. In the process of breaking, vibrations called “seismic waves” are generated. These waves travel outward from the source of the earthquake along the surface and through the Earth at varying speeds depending on the material through which they move. Some of the vibrations are of high enough frequency to be audible, while others are of very low frequency. These vibrations cause the entire planet to quiver or ring like a bell or tuning fork.

A fault is a fracture in the Earth’s crust along which two blocks of the crust have slipped with respect to each other. Faults are divided into three main groups, depending on how they move. Normal faults occur in response to pulling or tension; the overlying block moves down the dip of the fault plane. Thrust (reverse) faults occur in response to squeezing or compression; the overlying block moves up the dip of the fault plane. Strike-slip (lateral) faults occur in response to either type of stress; the blocks move horizontally past one another. Most faulting along spreading zones is normal, along subduction zones is thrust, and along transform faults is strike-slip.

Several fault lines run through the Carribean, but one transform fault is located right next to Port au Prince in Haiti.  Here is the location of this transform fault indicated by the green line.  The orange box is the center of the earthquake that occurred on Tuesday.

Once an earthquake occurs a measurement of the magnitude of the quake is given using the Richter Scale.  The earthquake in Haiti on Tuesday was measured at 7.0, which is a major quake.  The scale is logarithmic so that a recording of 7, for example, indicates a disturbance with ground motion 10 times as large as a recording of 6. A quake of magnitude 2 is the smallest quake normally felt by people. Earthquakes with a Richter value of 6 or more are commonly considered major; great earthquakes have magnitude of 8 or more on the Richter scale.

The map below shows the areas impacted by the quake…with the star being the center of the earthquake.  The center was just 10 miles from Port au Prince.

In looking back at past earthquakes along this fault line, it has been 140 years since it had produced a major earthquake.  While earthquakes do happen in this part of the Carribean, a major quake is quite rare.

Meteorologist Sally Severson talked with UW-Milwaukee’s Geo-sciences department today and they help explain why being on the fault line is a very precarious position.

Back in Wisconsin we are not immune to earthquakes, but most of us have never experienced one in our lifetime.  In looking back at past earthquakes to hit the state.  The one that occurred in 1947 seemed to be the most memorable for Milwaukee.  Here is a summary of that quake:

An earthquake on May 6, 1947, apparently centered just south of Milwaukee near the shore of Lake Michigan, caused only minor damage. There were no reports of injuries. The 4:25 a.m. CDT tremor shook buildings and rattled windows in many communities in a 7770 square kilometer area of southeastern Wisconsin. There were a few reports of broken windows at Kenosha (MM V), and residents of other communities reported that dishes and glasses had fallen from shelves. Some frightened Milwaukee residents ran into the streets in the belief there had been a serious explosion. The shock was felt in a 160 kilometer wide strip from Sheboygan to the Wisconsin – Illinois border and extended from the lakeshore to Waukesha, 40 kilometers inland.

For more information on the history of Wisconsin earthquakes, please check out the link below:

http://earthquake.usgs.gov/earthquakes/states/wisconsin/history.php

If you have any earthquake or weather related questions please post them in the comments section of the blog and either Mark or myself will be happy to answer them.  In the meantime, our weather will stay quiet today and tomorrow with highs in the 30s!  For the latest weather information make sure to tune into WISN 12 News today at 5, 6, & 10pm and follow us on Facebook at WeatherWatch 12

Jeremy Nelson

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