Category Archives: earthquake

Portland Between Scylla and Charybdis

MtHoodOutlookOn my return home from work yesterday I was greeted by the cover of the of this week’s issue of the Presbyterian Outlook with a beautiful shot of Mt. Hood from the south. Not often we get a literal active volcano on the cover of the Outlook.

But it serves as a reminder for those of us going to Portland for the 222nd General Assembly of the Presbyterian Church (U.S.A.) that from a natural hazard point of view Portland lies between Scylla and Charybdis, between a rock and a hard place, or to be geologically specific the Cascades and the Cascadia Subduction Zone.

To be very specific, the geologic hazards are dominated by a chain of active volcanoes on the east and one of the world’s great mega-thrust subduction zones on the west. Think Mt. St. Helens (which is not that far away) and the 2011 Fukushima earthquake. In particular, the Cascadia earthquake potential got a lot of publicity from a New Yorker article almost a year ago.

If you sense a certain amount of interest and enthusiasm on my part it has to do with the fact that these are the types of things I deal with in my day job as a geologist who specializes in seismic hazard analysis.

So what are we looking at? Well, the US Geological Survey has put together a nice little schematic cross-section of the Pacific Northwest that goes right through Portland and Mt. Hood.

subductionBasically, the sea floor is going down under Pacific Northwest and as it goes down the rocks heat up, magma is produced and comes to the surface in the Cascade range. As far as the volcanoes are concerned, they are clearly active. In Mt. Hood’s case it appears that Lewis and Clark missed the last big eruption by a bit over a decade, but reports of smoke and clouds later in that century are considered to be small eruptions from the mountain.

The good news, is that based on the current volcanic hazard assessments for Mt. Hood the mountain is far enough away that the most energetic products of a future eruption – lateral blast, pyroclastic flows, lava flows and lahars – would probably not directly affect Portland. The city would almost certainly get covered in airfall ash however.

And in case you are wondering, Portland is not unique. Here is a diagram of the last 4000 years of volcanic history for the Cascade Range from Wikipedia (and yes, I can say professionally that this chart is pretty good).

Cascade_eruptions_during_the_last_4000_yearsSo that is Scylla – the rock. What about Charybdis? What lurks in the deep blue sea?

The answer is a subduction zone capable of generating great earthquakes and accompanying tsunamis. The zone is long, it is wide and it is shallow – perfect conditions for a giant earthquake of around magnitude 9. We know because, among other reasons, one of these hit in January 1700. The indigenous peoples have legends about the earth shaking and the sea rising and inundating their villages. And while those accounts and geologic evidence give a narrow date range, the exact date of the earthquake on January 26th comes from Japanese records of a surprise tsunami that arrived with no shaking felt on those islands. Overall, there is evidence of seven great earthquakes in the last 3,500 years with a recurrence interval of between 300 and 400 years. And yes, with the last event 316 years ago we have entered that interval.

But what are the chances in a one week interval? Pretty low for both.  Doing a rough calculation including not just the mega-thrust but also the local faults around Portland, I get a probability of about one chance in 10,000 of damaging shaking during GA. And yes, one fault, the East Bank Fault, runs very close to the convention center. But if you want to be prepared, the Portland Bureau of Emergency Management does have their Survival Guide to the Big One online.

As for Mt. Hood – enjoy the great view. While there has been some recent new earthquake activity, it is minor and is not accompanied by other signs of impending volcanic eruption. Any critical activity would come with enough warning for us to get out of town before something big happens.

Now, if you want to use any of this natural activity and hazard as an analogy, metaphor or allegory for what might happen at the meeting well that is left as an exercise for the reader.

And if you need a final assurance that major geologic activity has a low probability of occurrence, you can look for me in Portland right there with you.

Have fun!

Earthquake in Nepal: Science And Response

It has been a while since I have made some scientific comments about an earthquake so for those of you who are not aware, I am an earthquake geologist and part of my day job is research and public outreach related to earthquakes.

Needless to say the earthquake over the weekend in Nepal got my attention and my response may be a bit surprising – no surprises here.

If you have been following the coverage you know that the most commonly reported magnitude measurement puts it at 7.8 although another slightly different magnitude measurement scale gives is a value of 8.1. For the record those of us in the business don’t spend a lot of time fretting the differences between the scales. Let’s just say that they all measure the event in slightly different ways and each has it’s advantages and disadvantages. The bottom line is that it is a big earthquake.

The most interesting scientific result to me is the finite fault model. This is a method of reconstructing the behavior of the earthquake as the fault breaks and it is interesting to note that the fault started breaking on the west end and broke to the east. In addition, the larger fault offsets were in the eastern portion and both of these circumstances would have increased the damage in the Kathmandu area. In addition, at 15 km deep it was relatively shallow and therefore more destructive. In addition, Kathmandu sits in a basin with soft sediments which would also amplify the shaking for a couple of different reasons. The circumstances of this quake were not in its favor.

You may have caught in the news coverage that there was a slightly larger earthquake in this area back in 1934 so these events do occur on a regular basis. There have been some other smaller earthquakes in the area but this event does overlap with both the 1934 event and the previous substantial event back in A.D. 1255. The Earth Observatory of Singapore has a nice page with a lot of technical information about the event. There is also a set of slides from IRIS (available in a PDF file) that gives a great overview of the event.

The bottom line is that this is a plate boundary where India is colliding with and going under Asia — very large earthquakes are to be expected. The Himalaya are being pushed up and Southeast Asia is getting squeezed out the side. In fact, this event moved Kathmandu about 10 feet south and raised the central Himalaya a little bit and Mt. Everest is most likely a bit taller, but think in terms of an inch, not feet. The majority of the motion is horizontal and this was a pulse in the constant shortening of Asia that is bringing Beijing closer to New Delhi. [Update: My initial uplift calculations were a bit off and Mt. Everest appears to be on the far side of the flexture line and is actually now an inch shorter.]

Aftershocks will continue for a while but with a couple in the magnitude 6 range and a good number of magnitude 5 events everything is looking typical. The big question is triggering and whether the stress redistribution of this event will make another large earthquake more – or less – likely. It would seem that triggering another earthquake is likely but it is best to think on the scale of decades to centuries and not a few days, months or years.

So what Presbyterian news has come out related to this?

First, branches are reporting on the status of their workers in that area: The missionaries from the neighboring Mizoram Synod are reported safe and have declined evacuation and will continue working there. Similarly, the Presbyterian Church in Ireland and the Church of Scotland have reported that their workers are safe and furthermore that all the workers with their partner agency, the United Mission to Nepal, are safe. And the Moderator of the Free Presbyterian Church of Northern Ireland returned from Nepal the day of the earthquake and the church reports that members and workers with the Free Presbyterian Church of Nepal are shaken but safe.

Second, work has kicked into high gear across the Presbyterian family to solicit relief aid for the country. A quick rundown:

I will keep updating that list as I hear of more branches who are reaching out with aid for that country.

As we look ahead prayers for the country are certainly in order. The death toll has passed 5,000 and based on the building styles and the disruption of communication with smaller villages I think the Prime Minister’s estimate of 10,000 dead is unfortunately a real possibility. Thank you for your prayers and however you can help out in this disaster.

Between A Rock And A Hard Place

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.

A New, Destructive, Earthquake Sequence In New Zealand

I am sure by now you have all heard about the destructive earthquake that hit Canterbury and Christchurch, New Zealand, yesterday.  When I heard the news on the radio my first reaction was that it was a strong aftershock of the 7.0 magnitude earthquake that hit that area last September, one month before the General Assembly of the Presbyterian Church of Aotearoa New Zealand was held in Christchurch.  (The PCANZ message on the new earthquake.) That opinion quickly changed as the damage reports started to appear in the media.  So here is a brief summary of what I know now.

The earthquake struck at 12:51 PM local time and was located just to the south of Christchurch.  While the 6.3 magnitude is significantly less than the 7.1 magnitude earthquake that occurred in September, the earlier event was some distance away in rural areas where the lower population density and single-family residential construction significantly reduced the cultural impact.  At the present time there are reports and pictures of significant damage in downtown Christchurch.  The death toll is currently at 65 but that is likely to rise as rescue efforts continue.  There are even reports of the shaking producing breaks and ice chunks to separate from a near-by glacier.

Besides the size and location, there is one other difference in the two earthquakes which may have increased the damage in this one.  While not as important as the close proximity to the urban center, yesterday’s earthquake was compressional, moving the ground upward.  The September quake was strike-slip, moving the ground sideways.  We will have to wait for the survey data to know how much the ground moved upward, but my initial calculation is about six to eight inches near the fault.  Looking at some of the pictures I think I see some of this compression but without the full context and exact location of the picture I can not be sure.  There is also discussion about this being a shallower earthquake than the September event and therefore more destructive.  Since that depth is generally only a measure of the start point of the earthquake I am not sure this is really a significant difference.  The September quake may have started deeper, but because of its size broke all the way to the surface.  Until we have detailed source-time functions for this event it will be difficult to really know the impact of the depth.

The question is asked if the two earthquakes are related.  My response is very likely yes, but exactly how I am not certain yet.  The most likely linkage is that September’s quake made this new one more likely through stress triggering.  A quick back of the envelope calculation last night indicated a good possibility, but I need to get better numbers today for the geometry of both quakes to be certain since it initially appears to fall right on a dividing line.  The second guess is triggering related to visco-elastic relaxation.  I’ll leave it at that.

It is interesting how the media grabs on to these stories and runs with them.  Without negating the impact of what is now being called one of New Zealand’s greatest natural disasters, it is important to keep this in perspective with other earthquakes.  I have heard news reports call this earthquake “huge.”  Is it huge?  Consider in the last 13 months we have had the Haiti earthquake – 7.0 magnitude with an uncertain death toll between 100,000 and 300,000.  We have also had the Chile earthquake one year ago – with an 8.8 magnitude it was one of the ten largest earthquakes of the last century.

These two earthquakes in New Zealand are a remarkable parallel to a couple we had here in SoCal and that I use in my class as a comparison of risk and hazard, and the different ways we measure the “size/impact” of an earthquake.  Back in 1992 the Landers earthquake hit an rural area (we call it desert) outside Los Angeles. While it was a significant earthquake at 7.3 magnitude and widely felt in the LA area, because of its location damage was fairly limited and there were only three deaths.  Two years later in 1994 the Northridge earthquake struck within the Los Angeles metropolitan area (“The Valley”).  It was a major, but smaller, earthquake at 6.7 magnitude but because it was in the heavily developed area the casualties were higher at 60 (higher by some counts) and the cost of damage was about 200 times higher than Landers.  (In the billions rather than millions of US$).  Location, location, location!

The parallel actually goes a bit further.  While they occurred further apart in space and time than the New Zealand quakes and are not linked in the same way, the Landers was a strike-slip earthquake like the September quake, and the Northridge was a compressional quake like yesterday’s.

Again, I in no way want to trivialize the death and destruction of yesterday’s quake and the continuing aftershocks.  In putting this in a seismological perspective I encourage prayers for all those affected and the rescue workers who are putting in hard and extended hours to help them.  I also ask for prayers for all others around the world who are impacted by natural disasters in their countries.

General Assembly 2010 Of The Presbyterian Church Of Aotearoa New Zealand

Spring is in the air and it is time for another General Assembly…

Of course, if it is Spring the Assembly would be in the Southern Hemisphere, and so we look forward to the convening of General Assembly 2010 of the Presbyterian Church of Aotearoa New Zealand at St. Andrew’s College in Christchurch in just a few hours.  It will conclude this Sunday October 3.

The theme of the Assembly is “Making Disciple-Making Disciples,” a topic chosen by the incoming Moderator, the Rev. Peter Cheyne.  As Rev. Cheyne says in the press release announcing the theme “It is about making disciples who become sufficiently mature to then make another generation of disciples.”  There is a booklet available on-line that will be used at the Assembly for six small-group Bible study discussion sessions on the topic.  Rev. Cheyne has started blogging, including a reflection on this topic.  (From a technical perspective it appears that the RSS feed is for the whole church web site and there is not one specific to his blog.)

So, for those GA Junkies playing along at home here is what you need to know:

Two important items I have not found yet are the docket and an on-line news page.  I will update here when I do find them. But this is a note that there will be audio files available of certain events so keep an eye out for that. UPDATE: The News and Audio Page is now being updated.

Similarly, I have been searching but have not found anyone tweeting the GA, officially or unofficially, and no hashtag.  Again, will update if I find anything.

The back story to this GA is the September 4 magnitude 7 earthquake near Christchurch.  For those not familiar with earthquake behavior the aftershocks behaviour is very typical (GNS calls it “textbook“) and they continue with five in the magnitude 3 range in the last day reported by the GeoNet official agency information.

Since the earthquake there have been a number of information reports and updates from church-related sources.  Linked to the GA web page is an update related to the Assembly.  And thanks to notes from the Rev. Geoff King of Knox Church, Christchurch, as well as the Presbyterian Research blog for posting the accounts, we have Pastor King’s three updates about the situation after the earthquake with one that day, another the next day, and the last a week on.  (That is the ecclesiastical perspective, for the geological angle I really appreciated the great photos of faulting that GNS has up on their scientific response page.)

So in the same way that prophet Amos marks time with an earthquake in his day this GA will probably be remembered for its temporal and geographical proximity to the Darfield earthquake.

Stay tuned in the coming week and let us see what God does among his people as they meet on the South Island.  Prayers for the meeting.

Magnitude 7.2 Earthquake Near Christchurch, New Zealand

In an interesting intersection of my seismological work and my GA work about an hour ago a 7.2 magnitude earthquake struck Christchurch , New Zealand.  There are initial reports of peak ground accelerations above 0.4%g and very strong intensities so significant damage can be expected.  While the mainstream media is trying to get information on this the twitterverse is indicating sections of the city with major damage.  Confirmation will await 1) the light of day and 2) the ability to get news out of the epicentral region.

I mention the intersection with Presbyterianism because the 2010 General Assembly of the Presbyterian Church of Aotearoa New Zealand is scheduled to convene in Christchurch on the 30th of this month.

Prayers for all affected and we will have to wait and see how this will impact the GA.

Technical note:  The South Island of New Zealand has a geologic and tectonic setting similar to California with a plate-bounding strike-slip fault running through it.  While this was not on the Alpine fault, having an earthquake like this on a near-by fault is not a geologic surprise.  Again, we are working with the scientific information we have and it will take a while to fully characterize this event.

UPDATE: Presbyterian Research passes along a description and message from a pastor in the area

Great Earthquake In Chile – Feb. 27, 2010

The aftershocks just keep on going… And will keep on going for a while.

When I got up Saturday morning and turned on my cell phone it immediately filled up with text messages and after clearing those there were a bunch more.  Yup, my day job caught up with me on the weekend and after an event Saturday morning I spent the afternoon studying the developments and looking at the tectonics.

The basic information: The magnitude 8.8 earthquake off the coast of Chile was a shallow earthquake in the Peru-Chile trench and appears to have broken about 400 miles of the fault.  The fault is the boundary between the South American Plate and the Nazca Plate.  The Nazca Plate is a small and young tectonic plate completely under the Pacific Ocean.  The Nazca Plate is going under South America at about 80 mm/year and is responsible for the Andes Mountain Range and the active volcanoes in it.  At the time of this writing there have been 119 aftershocks of magnitude 5 or larger with an additional one now every hour or so now.

This earthquake makes the top ten list of events since 1900 and released about 500 times more energy than the recent earthquake in Haiti.  With the official death toll in this event still a bit below 1000 (it will certainly pass that mark) it is interesting to note the difference that preparedness and economic development have on earthquake survivability.  There is substantial damage and I spent a lot of time studying the failure modes that I see in a great collection of pictures by the Boston Globe, but I don’t see the total collapse of neighborhoods full of unreinforced masonry structures like the pictures from Haiti showed.

The Pacific Coast of South America is no stranger to great earthquakes. (And for the record, a “great earthquake” is a technical term to distinguish an even of magnitude 8 or larger.  There is a magnitude 8 or larger earthquake somewhere on the earth about every year and a half on average.)  The largest recorded earthquake was the 1960 Chile earthquake (magnitude 9.5) on the section of the fault just to the south of this earthquake.  And Charles Darwin experienced a large earthquake here while visiting on the voyage of the Beagle in 1835.

For an idea of the size of this earthquake consider the fact that the point the earthquake began (the epicenter) was about in the middle of the section of fault that broke.  As the earthquake happened it broke about 300 km in each direction.  At a rupture speed of 3 km/sec that give a rupture time of 100 seconds.  That is how long the fault took to break, but it generates different waves that travel at different speeds so the local shaking is longer as all those waves go by.  Another point of comparison is that we would expect the largest aftershock to be about the same size or slightly larger than the Haiti earthquake.  At the present time the largest aftershock is magnitude 6.9 and Haiti was magnitude 7.0.

Now the reminder for my North American readers:  Many of you are probably aware that Alaska had a great earthquake like this one back in 1964 that devastated southern Alaska, especially the Anchorage area.  There is a lesser known earthquake back on January 26, 1700 along the coast of Northern California, Oregon, Washington and British Columbia.  While this event is detailed in the oral traditions of the indigenous peoples of the area we also have a written record from Japan of the devastation caused by the tsunami there.  And the geologic situation in the Pacific Northwest is very similar to South America with the volcanic mountain range (Cascades) and a small, young tectonic plate (the Juan de Fuca Plate) going underneath North America.  It is good to know that locally this risk is now understood and preparedness measures are being taken.