Well, it is not exactly Scylla and Charybdis, but the Mid-Atlantic states of the U.S. found themselves in the shaking of a moderate earthquake Tuesday while keeping a watchful eye on Hurricane Irene.

I want to talk about the relative risks later in this post, but first a little bit on the earthquake itself.

As you can probably imagine Tuesday was an interesting day at work for me.  The day began with hearing about the other significant earthquake in Colorado. When I heard about it on the radio I was expecting it to be a bit further west in the more active seismic belt where I have worked (fifth from top and third from bottom if you really care).  But I found it was to the east along the front of the Rocky Mountains.  An interesting location but not completely unexpected.

Then about 11 AM PDT my computer ground to a halt.  Checking around I found that my Twitter feed for earthquakes had gone crazy and that a 5.8 had occurred back on the east coast.  At about the same time my email sprung alive with notes from college friends with questions or comments.  Now here was an interesting event. And it was the largest earthquake globally on Tuesday.

For a comparison of this earthquake to previous eastern US events you can have a look at the USGS Historic Earthquake list.  The largest east coast earthquake is the 1886 Charleston, SC, earthquake at 7.3 and there are no other east coast earthquakes over 7 on the list. There are no earthquakes on the list in the magnitude 6 range. The next earthquake is an 1897 event in western Virginia which appears to still hold the record as the largest earthquake in the state. In total there are thirteen earthquakes in the magnitude 5 range in the coastal states.  Then there are seven more earthquakes for which there is not complete enough information to accurately estimate a magnitude, but we know that the intensity of shaking was strong enough that we can safely consider them to also be in the magnitude 5 or larger range.

So, for the eastern seaboard that are 21 earthquakes in about 300 years or an average of one earthquake about every 14 years. The previous one? Nine years ago in northern New York.

It is interesting to look at the seismic hazard map for the contiguous United States.  An experienced Presbyterian will appreciate the seismic hazard zones for the central and eastern US.  With only a few exceptions we don’t know where major deep faults are and which of the myriad of faults are inactive and which might be reactivated. Therefore, where there is higher seismic hazard is where something has happened in the past, just like some sections of the Book of [Church] Order are there because something happened. In that part of the world seismic hazard analysis is reactive.

The western US is a different story.  We think we know where active faults are, can measure their activity and put hazard estimates on specific geologic features and not just broad areas. Hazard zones are more narrowly defined and we believe have better known values.

So with that quick intro to seismic hazard estimation, lets consider how it compares to other natural hazards.  The bottom line for much of the country is that earthquakes are the least of your worries.

A good comparison comes from an analysis by Barton and Nishenko for the USGS. They find that for the United States the probability of having 10 fatalities for an event in a given year is 11% for an earthquake, 39% for a hurricane, 86% for floods, and 96% for tornadoes. For a graphical representation of where you would expect these consider this map from Insurance Center Associates. There is a similar one from the New York Times. (And it is worth pointing you to Robert Simmon’s critique of how this map represents the data.)

Now, let me make what will seem at first to be a quantum leap…

One of the thing’s I appreciate about our Reformed heritage is the concept of Vocation. What this means in my field is that when I talk to people about earthquakes I recognize that there are usually emotional issues underlying many of the questions they ask me.  In a sense, I am not just an earthquake geologist but I become a counselor or therapist as well.  In other words, I am doing ministry in a particular and unique way.

What I have found in doing this is that to a given individual the type of natural disaster is just as important as the risk of a disaster itself.  It is clear to me from talking with dozens of people that the different numbers only matter to a point and that people have different personal comfort levels with different types of risks. This is brought home nicely in a split-panel cartoon that ran right after the Northridge Earthquake — in one panel a guy is up to his eye balls in snow reading a newspaper headline saying “Earthquake hits California” and in the other panel a Californian, with debris behind him, is reading the headline “Record Cold Grips Northeast.” And each of them is thinking “Why would anyone live there?”

Why would anyone live in earthquake country? Because they don’t like tornadoes, hurricanes or blizzards.  Likewise, I know people who have left California for the Midwest because they are more comfortable with tornadoes than earthquakes.  Some people like predictability. Some hate waiting for the unknown in a tornado warning and would rather not have the suspense and have an earthquake hit out of the blue.  Some have a sense of security knowing that hurricanes have a season when they hit and you get two days notice.  Some would rather have an earthquake and get it over with.  I think that I have heard it all.

Likewise I sometimes wonder if different Presbyterians have preferences for different risks in the church. I will leave the development of that idea as an exercise for the reader.

So to those between the rocking of the earthquake and the hard place of the hurricane, may you know God’s solid presence in the midst of earth’s uncertainty. To all of those who are in the path of Irene, whether it has already gone through you or is still headed your way, we lift our prayers.  To those in the epicentral region of the earthquake we pray that your damage is not substantial and is easily repaired and give thanks that there was no loss of life and no serious injuries. To those currently meeting in Minneapolis we pray that no tornadoes will go through town. And to all affected by the many different types of natural disasters we pray for God’s comfort and peace for you in the midst of it.