Dodged a Bullet
It looks like the Chileans and southern Peruvians dodged a bullet in the northern Chile seismic gap. The 8.2 earthquake yesterday didn’t fill the gap, and the tsunami maxed out locally at ~ 2.3 m or so. Some damage to the airport and container facilities at the mining port of Iquique, and a few casualties. Otherwise, the widespread evacuations were largely not needed, and damage was light. The workshop I was at in Santiago in late January was focused on this exact spot, which probably was near the site of an M9 earthquake in 1868. After Sumatra and Tohoku, areas previously though unlikely to generate M9 earthquakes are now suspect, and the not very well known 1868 Arica event is an example of a very large earthquake that never fit the older seismological models.
The 1868 Arica event generated a 12-16m tsunami locally, and one up to 7m in New Zealand! Yikes. But given the likely slip deficit, that is the seismic gap is not filled, there remains some possibility of another large event in the near future, triggered by this one and distinct from the aftershock sequence. Something like this may have happened with two events in 1868 and 1877.
The focal mechanism for the April 2014 event is as expected, a shallow thrust well aligned with the strike of the Nazca-S. America megathrust:
April 1, 2014, NEAR COAST OF NORTHERN CHILE, MW=8.1
Meredith Nettles
Goran Ekstrom
CENTROID-MOMENT-TENSOR SOLUTION
GCMT EVENT: C201404012346A
DATA: II LD IU DK CU MN IC G GE
KP
L.P.BODY WAVES:159S, 393C, T= 50
MANTLE WAVES: 159S, 451C, T=200
SURFACE WAVES: 142S, 199C, T= 50
TIMESTAMP: Q-20140401232631
CENTROID LOCATION:
ORIGIN TIME: 23:47:29.1 0.1
LAT:19.77S 0.01;LON: 70.98W 0.01
DEP: 21.9 0.4;TRIANG HDUR: 26.9
MOMENT TENSOR: SCALE 10**28 D-CM
RR= 0.940 0.004; TT=-0.037 0.002
PP=-0.903 0.003; RT= 0.595 0.023
RP=-1.270 0.030; TP= 0.201 0.001
PRINCIPAL AXES:
1.(T) VAL= 1.702;PLG=61;AZM= 58
2.(N) -0.024; 6; 159
3.(P) -1.678; 28; 252
BEST DBLE.COUPLE:M0= 1.69*10**28
NP1: STRIKE=357;DIP=18;SLIP= 109
NP2: STRIKE=157;DIP=73;SLIP= 84
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eqgold
atquake 
[…] Chris Goldfinger, a seismologist at Oregon State University whose focus is offshore faults like Chile’s and the Cascadia fault off the Northwest Coast, posted a piece on Chile’s “dodged bullet.” […]
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Another Warning for the Northwest From Chile's Earthquake Hot Zone | NEWS.GNOM.ES
April 2, 2014 at 7:00 pm
Hi Ted,
Good question, I was thinking about that last night. The 8.2 in Chile is I think very similar to many of the southern Cascadia events we see in the paleoseismology. We know that about half of those (~ 10) were too small to leave deposits in Bradley Lake, so they were less than ~ 5m in height. The maximum tsunami height I’ve seen at Iquique is about 2.3 meters, so if this had happened here, there would likely be little or no geologic record of it on land. Offshore, this is probably recorded as a thin silty turbidite, similar to those offshore Oregon that we’ve inferred to be about the same magnitude based on rupture length and estimated width. In January I was in Santiago for a workshop on this area, the northern Chile seismic Gap, and we spent quite a while discussing what avenues might work to pull a paleoseismic record out of the area, and there aren’t many. No coastal lake or marshes to speak of, desert environment etc. Offshore may hold a record though.
Thanks for posting the video! One lesson from this is that Chile is a bit better prepared then the PNW, so the same earthquake here would likely damage URM buildings like many of the schools, at least along the coast.
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eqgold
April 2, 2014 at 3:59 pm
Hi Chris, thanks for the perspective on yesterday’s event near Iquique. Question: how close is the analogy to a Southern Margin event in Cascadia? Given the probability of that event based on the histories you have compiled, seems like we should be quick to seek and apply lessons here when the Earth supplies them.
Here’s a short video you will enjoy, based on good progress in a few Portland schools. It was written and produced by three Portland high school students:
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Ted Wolf
April 2, 2014 at 3:37 pm