Minnesota earned its 'blue mark' in the 1975 Morris earthquake, which had its epicenter in the western part of the state.
- Californians, want to run away from the Big One? Head for Minnesota.
- As this map shows, the Gopher State is the least likely to be hit by earthquakes.
- Choose your new home wisely, though: even Minnesota has one earthquake-sensitive spot.
Not if, but when
The Long Beach earthquake hit on 10 March 1933 with an estimated magnitude of 6.25 on the Richter scale.
Image: Nathan Callahan, CC BY 2.0
It's not if, but when: Californians live with the certainty that someday, the Big One will hit.
The Big One is an earthquake with a magnitude of at least 7.8 on the Richter scale. Because of the plate tectonics at work under California, big quakes like that hit the area every 45 to 230 years.
The last one was more than 160 years ago. That's why paleoseismologist Kerry Sieh says the next one is likely to happen "within the lifetime of children in primary school today."
Here's how the United States Geological Survey (USGS) rates the hazard of a major earthquake in California in the next 30 years:
- 60% chance of a 6.7-magnitude quake.
- 46% chance of a 7.0-magnitude quake.
- 31% chance of a 7.5-magnitude quake.
The earthquake hazard map of the United States.
Image: USGS, public domain
The Pacific coast is purple: the highest hazard. The entire west is shaded in colors denoting declining hazard. Only relatively small parts of the country are covered by the zone of lowest hazard:
- central and southern Texas;
- most of Florida, Michigan, Wisconsin, Iowa, and North Dakota;
- sizable chunks of Kansas, Nebraska, Montana, and South Dakota;
- and tiny bits of Alaska, Colorado, New Mexico, Louisiana, Arkansas, Alabama, and Georgia.
One state seems hazard-free, but that's only until you notice the blue spot in Minnesota's western bulge.
So, what do these colors actually denote? Earthquake hazard maps show the potential shaking hazard from future earthquakes.
The USGS defines earthquake hazard as the probability of ground motion over 50 years. That probability is determined by a region's geology and earthquake history.
The location of fault lines alone is not enough to determine quake hazard: a large earthquake can produce tremors at a relatively large distance from the actual fault line.
The colors on this earthquake hazard map correspond to Seismic Design Categories (SDCs), which reflect the likelihood of seismic activity leading to ground motion of various intensities.
Damage caused by the 6.0-magnitude Napa County earthquake of 24 August 2014.
Image: Matthew Keys, CC BY-SA 4.0
These SDCs are used to determine the level of seismic resistance required in building design and building codes.
- SDC level A (grey): Very small probability of experiencing damaging earthquake effects.
- SDC level B (blue): Moderate-intensity shaking possible. Such shaking will be felt by all. Many will be frightened. Some furniture will be moved and some plaster will fall. Overall damage will be slight.
- SDC level C (green): Strong shaking possible. Damage will be negligible in well-designed and well-constructed buildings; considerable in poorly-built structures.
- SDC levels D0 (yellow), D1 (orange) and D2 (red): Very strong shaking possible. Damage will be slight in specially designed structures; considerable in ordinary substantial buildings, with partial collapse; and great in poorly built structures.
- SDC level E (purple): This is near major active faults capable of producing the most intense shaking. Even in specially designed structures, the damage will be considerable. The shaking is intense enough to completely destroy buildings.
The Morris quake
Minnesota earned its blue spot in 1975.
Image: USGS, public domain
This earthquake hazard map is not a snapshot of the past, but an evolving prediction of the future. The map is adapted as geological knowledge increases. But it is also partly based on past events – or more precisely the likelihood of their recurrence.
Minnesota earned its blue spot from the 1975 Morris earthquake. With its epicenter in Stevens County, it struck at around 10 am on July 9th of that year and had a magnitude of 4.6. It was the first seismic event recorded in the state since the Staples quake of 1917, and it was felt as far afield as the eastern Dakotas and northern Iowa.
Near the epicenter, plaster cracked and pictures fell off walls. In the town of Morris, two homes suffered damage to their foundations. Not quite California-sized, but for lack of comparison, probably Big Enough for the locals.
Strange Maps #1011
Got a strange map? Let me know at email@example.com.
A new study looks at how to make a successful smile.
Do you have a good smile? It is perhaps our most significant instrument of nonverbal communication that can go a long way in smoothing out social interactions. It is also of interest to scientists who are trying to figure out how our facial expressions affect others. A new study found that there is what's called "a successful smile" - the one that gets the best response.
Researchers, led by Professor Nathaniel Helwig from the University of Minnesota, showed a series of 3D faces generated on a computer to 802 study participants. The faces had slightly different expressions, with variations in the mouth angle, the size and symmetry of the smile, and how much of the teeth you could see.
Here's how the scientists explained what these criteria were (based on the drawing below):
"Mouth angle is the angle between the green and blue lines. Smile extent is the length of the green line. Dental show is the distance between the lower and upper lips."
Definitions of the spatial parameters used in the study. Credit: Nathaniel E. Helwig, Nick E. Sohre, Mark R. Ruprecht, Stephen J. Guy, Sofía Lyford-Pike.
The study's subjects rated the smiles on how effective, genuine and pleasant they appeared as well as what participants thought was the emotional intent behind each smile.
What's perhaps counterintuitive about these new findings is that a "successful smile" does not mean it's the biggest, most teeth-baring, ear-to-ear grin. A smile that is most effective and genuine has to have a balance of teeth, mouth angle and extent to hit what the researchers called "the sweet spot". But within that prescription, there is variation in how those elements are combined. There is not just one way to have a well-received smile.
Smiles that were rated the highest were also developed symmetrically, with the left and right sides of the face synced up in no more than 125 milliseconds. Interestingly, slightly asymmetrical smiles were found to be even more attractive. The same held true for very wide smiles with fewer teeth. Smaller smies, without much of a curve were interpreted by the subjects as contemptuous. Too much smile angle and extent was deemed fake or creepy. A bigger smile isn't necessarily better.
Smile 22 with various amounts of timing (delay) asymmetry.
The researchers hope to use their findings to develop a stronger understanding of how we read the faces of others. The study can also lead to advancements in facial reanimation and reconstruction surgery.
You can read the study in the journal Plos One.