I am a New Jersey native, living in the New York metro area. This article describes my experience from the effects of the Mid-Atlantic earthquake which occurred on August 23rd, 2011. I reference the colossal earthquake that struck Japan on March 11th, 2011, and I articulate aspects of the warning system and lead time with tornadoes in the U.S. and with earthquakes in Japan.

1. On the afternoon of August 23rd, 2011, an earthquake rocked the Mid-Atlantic region. Seismographs picked up
its signature at 1:51 PM as it measured a magnitude of 5.8 on the Richter scale. The epicenter of the seismic
discharge was located in northern Virginia, 38 miles northwest of Richmond. The shock waves from the
subterranean shift were felt in areas of New Jersey, as far north as Montreal, Quebec, east to Rhode Island
and as far south as Georgia.
It was a few minutes before 2 o’clock when I experienced the effects of the tremor (I was in my New Jersey
apartment at the time). At first, I looked out the window to see if there was a strong gust or a nearby truck that
could have generated the vibration. As the shaking gained momentum, I suspected it was an earthquake: how
long would it last, how intense would it be, what danger was I in…there was no way to tell.
My cat was in the bedroom seemingly unable to move: her arms and legs were spread out as if to prevent
herself from sliding. I picked her up, moved under the doorframe of the bathroom and waited for the seismic
impulse to pass. As I braced my arm against the doorframe, I noticed the initial vibration gave way to a gentle
sway: the resonance continued to build as if the apartment was slowly, rhythmically swinging on a giant
pendulum. The standing picture frames were shaking in synchronization; all the while, I heard a low rumbling
coming from outside. In the bedroom, the remote control hooked to the fan tower fell…at that moment the
rocking stopped. It was silent for a few moments following the tremor then a commotion of startled residents
descended outside. The entire event lasted about 30 seconds, but it seemed to unfold in slow motion.
I checked online and turned on the television to the local channel—an earthquake was confirmed. Many
people I spoke with in the Tri-State area experienced the tremor. My brother was in his house a few minutes
north of me, yet he did not feel the effects from the propagating vibrations. A friend living in Kentucky, west of
the epicenter, did not notice the event.
Although the Virginia quake was moderate in size (magnitude 5.0 – 5.9), the seismic waves traveled further
distances, its effects were more intense, compared with California tremors of equal size. Unlike the West
Coast, which sits between two sliding plates, the Eastern U.S. is situated in the middle of the North American
plate. The earth’s crust in the Eastern U.S. is more solid and dense, aiding in the propagation and
amplification of the vibrations (the shaking). Seismic waves travel faster through solid rock like granite
compared to gravel and soil. When subjected to strong shaking, moist sediment like silt (fine sand) becomes
susceptible to liquefaction (process by which a solid behaves like a liquid).
Predicting the magnitude (size), intensity (effects), when and where an earthquake will hit is different from
forecasting severe weather events such as tornadoes. U.S. meteorologists use Doppler radar to identify
Tornadic Vortex Signatures (TVS), bow echoes and hook echoes from mesocyclones—as the event takes
shape. Recent improvements in technology and training have led to a lower average lead time of 11 minutes
for tornado warnings.
Japan has the most advanced early warning system for earthquakes. On March 11th, 2011, Japan broadcast a
nationwide alert within seconds after the powerful quake was detected, yet Tokyo residents had a lead time of
just 80 seconds before the devastating tremor reached the city. Why? The answer lies in the propagation
velocity of seismic waves. Although tsunamis can reach speeds between 500 and 700 miles per hour, seismic
waves move much, much faster.
More about the velocity in a moment; let’s go over the four main types of seismic waves. Primary or P-Waves
compress and dilate the medium (i.e. rock; soil) in which it passes through as it propagates in the direction of
the underground force. Secondary or S-Waves oscillate perpendicular to the horizontal momentum of energy
—up and down and side-to-side. P-Waves and S-Waves are referred to as body waves because it radiates
through the Earth’s body (from the hypocenter below the surface). The other two distinct seismic vibrations are
Love Waves and Rayleigh Waves, which are referred to as surface waves because it travels along the Earth’s
surface (from the epicenter). Love Waves shift the ground side-to-side as it moves forward. Rayleigh Waves
roll along the vertical axis in an undulating motion.
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2. The shorter P-Waves cause little to no damage, and are often too faint to be felt by people (some animals such
as dogs and elephants can sense vibrations from P-Waves). The longer S-Waves are typically the first
vibrations we experience. S-Waves are capable of causing ground shifts and structural damage to buildings.
Love Waves and Rayleigh Waves are more intense, causing the most damage, because the vibrations radiate
along the ground instead of below the surface.
With respect to propagation velocity, P-Waves are the fastest, followed by S-Waves then Love Waves and
Rayleigh Waves. Put another way: body waves radiate more quickly than surface waves. The average
velocity of an S-Wave is 2.5 miles per second; its speed varies depending on the composition of the Earth’s
crust. Located 230 miles southwest of the epicenter, Tokyo residents would have experienced the S-Wave
from the March 11th quake in about 90 seconds.
The average speed of a tornado is 30 miles per hour; the fastest twisters travel 60 – 70 miles per hour. To put
it into perspective, I felt the shock waves approximately 4 minutes after the Virginia earthquake struck. The
epicenter was about 330 miles southwest of my location—that is an average speed of 5,000 miles per hour! In
retrospect, the vibrations and effects from the Mid-Atlantic tremor were a series of distinct seismic waves
arriving one after another.
Side note: News and social media coverage of the Virginia earthquake was non-stop until the attention shifted
to the approach of Hurricane Irene. 12 hours earlier at 1:46 AM EST on August 23rd, a quake, magnitude of
5.3, rattled Colorado (centered 180 south of Denver). It was the second tremor originating from the same
location within a 7-hour period (first temblor, magnitude 4.6, struck at 7:30 PM EST on August 22nd). There
was not as much coverage in the Denver news media or on twitter regarding the back-to-back events.
Earthquakes of magnitude 5+ are uncommon east of the Rocky Mountains. The highest risk for seismic
activity east of the Rockies is in the Ozark region.
This table lists the magnitude, description, effects and frequency of earthquakes based on observations since 1900.
Magnitude Description Earthquake effects Frequency of occurrence
< 2.0 Micro Micro earthquakes, not felt. Infinite number
2.0–2.9 Generally not felt, but recorded. 1,300,000 per year (est.)
Minor
3.0–3.9 Often felt, but rarely causes damage. 130,000 per year (est.)
Noticeable shaking of indoor items, rattling noises.
4.0–4.9 Light 13,000 per year (est.)
Significant damage unlikely.
Can cause major damage to poorly constructed buildings.
5.0–5.9 Moderate 1,319 per year
At most slight damage to well-designed buildings.
Can be destructive in areas up to about 160 kilometers
6.0–6.9 Strong 134 per year
(99 miles) across in populated areas.
7.0–7.9 Major Can cause serious damage over larger areas. 15 per year
8.0–8.9 Can cause serious damage in areas several hundred
1 per year
Great kilometers across.
9.0–9.9
Devastating in areas several thousand kilometers across. 1 per 10 years (est.)
Never recorded, widespread devastation across very large Extremely rare
10.0+ Massive
areas; see below for equivalent seismic energy yield. (May not be possible)
Magnitude vs. Ground Motion and Energy
Magnitude Ground Motion This table shows that a magnitude 7.2 earthquake
Change Change Energy Change produces 10 times more ground motion than a
1.0 10.0 times about 32 times magnitude 6.2 earthquake, and it releases about
32 times more energy. The energy release reflects
0.5 3.2 times about 5.5 times
the destructive power of a quake.
0.3 2.0 times about 3 times
0.1 1.3 times about 1.4 times
This article can be viewed here as well, along with other articles I have written and seeded on jp-thoughts.newsvine.com.
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3. Sites visited / links viewed in researching information and referencing tables for this article
Date (mm/dd/yy) posted for articles; and seismic event along with state; country: magnitude/depth.
http://allshookup.org/quakes/wavetype.htm
http://aspire.cosmic-ray.org/labs/seismic/index.htm
http://churmura.com/lifestyle/environment/earthquake/20286/ (10/21/09)
http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php
http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php
http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0001xgp/ (03/11/11 JP: 9.0/18.6 miles)
http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0005ic9/ (08/22/11 CO: 4.6/3.1 miles)
http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0005idz/ (08/23/11 CO: 5.3/2.5 miles)
http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0005ild/ (08/23/11 VA: 5.8/3.7 miles)
http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usb0001igm.php (02/21/11 NZ: 6.1/3.7 miles)
http://earthquake.usgs.gov/learn/facts.php
http://earthquake.usgs.gov/learn/faq/?categoryID=2&faqID=114
http://earthquake.usgs.gov/learn/topics/mag_vs_int.php
http://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunami
http://en.wikipedia.org/wiki/2011_Virginia_earthquake
http://en.wikipedia.org/wiki/Plate_tectonics
http://en.wikipedia.org/wiki/Plate_tectonics#Types_of_plate_boundaries
http://en.wikipedia.org/wiki/Richter_magnitude_scale
http://en.wikipedia.org/wiki/Seismic_wave
http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html
http://physics.info/intensity/
http://science.howstuffworks.com/environmental/earth/geophysics/question142.htm
http://science.howstuffworks.com/nature/natural-disasters/tsunami3.htm
http://tremblingearth.wordpress.com/2011/03/04/liquefaction-in-new-zealand/ (03/04/11)
http://wcatwc.arh.noaa.gov/physics.htm
http://www.alphadictionary.com/goodword/word/temblor
http://www.answers.com/topic/what-factors-affect-the-average-duration-of-an-earthquake
http://www.britannica.com/EBchecked/topic/532925/seismic-wave
http://www.csmonitor.com/Innovation/Latest-News-Wires/2011/0314/Japan-earthquake-How-Tokyo-got-an-80-
second-head-start (03/14/11)
http://www.differencebetween.com/difference-between-earthquake-magnitude-and-vs-intensity/ (03/12/11)
http://www.geo.mtu.edu/UPSeis/magnitude.html
http://www.geology.siu.edu/people/pinter/pdf/EQMagIntensity.pdf
http://www.moorlandschool.co.uk/earth/images/Earthquakefaq.htm#FAQ17
http://www.nj.com/news/index.ssf/2011/08/earthquake_rocks_new_jersey_an.html (08/23/11)
http://www.npr.org/blogs/thetwo-way/2011/08/23/139892996/why-a-quake-in-virginia-isnt-as-rare-as-it-sounds?
ft=1&f=1001 (08/23/11)
http://www.nytimes.com/2011/03/12/world/asia/12japan.html?pagewanted=all (03/11/11)
http://www.scientificamerican.com/article.cfm?id=fast-facts-japan
http://www.theblaze.com/stories/why-was-virginias-earthquake-felt-all-the-way-in-canada/ (08/23/11)
http://www.time.com/time/world/article/0,8599,2059780,00.html (03/18/11 Japan’s Warning System)
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