Illinois' 5.2 EarthCache
Hidden : 4/21/2008
Difficulty:
1.5 out of 5
Terrain:
1 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Epicenter of Illinois' recent 5.2 Earthquake.

Welcome to an epicenter. On Friday, April 18, 2008 at 04:36 AM, Illinois and most of the midwest was awakened to a rare Wabash Valley Earthquake measuring a magnitude of 5.2 on the Richter Scale. The earthquake originated 7.2 miles below ground. There has also been several aftershocks with one measuring 4.6 on the Richter scale.

Source: U.S. Geological Survey and Illinois Geologial Survey. website: http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2008qza6.php#summary

The following is a release by the United States Geological Survey, National Earthquake Information Center: An earthquake occurred 35 km (20 miles) SW of Vincennes, Indiana and 205 km (125 miles) SW of INDIANAPOLIS, Indiana at 3:36 AM MDT, Apr 18, 2008 (4:36 AM CDT in Illinois). The magnitude and location may be revised when additional data and further analysis results are available.


Felt Reports
Reports of minor structural damage in West Salem, Illinois and Louisville, Kentucky. Felt over a wide area of the central United States with felt reports as far west as Kansas, as far north as the Upper Peninsula of Michigan and as far south as Georgia.


Tectonic Summary

EARTHQUAKES IN THE WABASH VALLEY SEISMIC ZONE
These earthquakes occurred in the Wabash Valley Seismic zone. The earthquakes in this zone are scattered over a large area of southeastern Illinois and southwest Indiana. The zone had at least eight prehistoric earthquakes over the past 20,000 years with estimated magnitudes ranging from about 6.5 to 7.5, based on geologic evidence. Earthquakes of the size of the recent quake (Mw 5.2) can produce smaller aftershocks over the following days. A few might be large enough to be felt. Typically, earthquakes of this size (Mw 5.2) can cause light damage within a few tens of miles from the epicenter. Central and eastern US earthquakes generally shake areas about 10 times as large as those that occur in California. It is not surprising that this earthquake was felt as far south as Florida.

The Wabash Valley Seismic zone is adjacent to the more seismically active New Madrid seismic zone on the seismic zone's north and west. The recent earthquake is also within the Illinois basin - Ozark dome region that covers parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas and stretches from Indianapolis and St. Louis to Memphis. Moderately frequent earthquakes occur at irregular intervals throughout the region. The largest historical earthquake in the Illinois Basin region (magnitude 5.4) damaged southern Illinois in 1968. Moderately damaging earthquakes strike somewhere in the region each decade or two, and smaller earthquakes are felt about once or twice a year.

Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).

FAULTS Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most bedrock in the Illinois basin - Ozark dome region was formed as several generations of mountains rose and were eroded down again over the last billion or so years.

At well-studied plate boundaries like the San Andreas fault system in California, scientists can often determine the name of the specific fault that is responsible for an earthquake. In contrast, east of the Rocky Mountains this is rarely the case. The Illinois basin - Ozark dome region is far from the nearest plate boundaries, which are in the center of the Atlantic Ocean, in the Caribbean Sea, and in the Gulf of California. The region is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths. Accordingly, few earthquakes in the region can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake. As in most other areas east of the Rockies, the best guide to earthquake hazards in the Illinois basin - Ozark dome region is the earthquakes themselves.


What is an earthquake? An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.

Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens. The largest, main earthquake is called the mainshock. Mainshocks always have aftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock!

What causes earthquakes and where do they happen? The earth has four major layers: the inner core, outer core, mantle and crust. The crust and the top of the mantle make up a thin skin on the surface of our planet. But this skin is not all in one piece – it is made up of many pieces like a puzzle covering the surface of the earth. Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other. We call these puzzle pieces tectonic plates, and the edges of the plates are called the plate boundaries. The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.

Why does the earth shake when there is an earthquake? While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us!


The coordinates will take you to an intersection closest to the epicenter of the 5.2 quake. Also the center of the 4.6 aftershock is just 2 miles North near the same road.

To claim a log on this Earthcache:
1. Take your picture at the coordinates and post it with your log.

2. In your log please state if you felt the Earthquake on Apr. 18, at 4:36 AM and how many miles away from this location were you at the time?

3. Email me with answers to the following questions within 3 days of your log: DO NOT POST THESE IN YOUR LOG even if encrypted, Email answers only.

a. What is the elevation reading at the coordinates?
b. Describe the topography around the epicenter(ie. flat?, hilly?, rocky?, any creeks or streams nearby?, etc.)
c. What is the difference between an epicenter and a hypocenter?
d. What are the 3 types of "shocks" that can be felt.
e. Name the 2 Seismic Zones that affect Illinois.

If these requirements are not met your log will be deleted.

Additional Hints (No hints available.)



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