Well, not completely dodged…

While casualties and damage from the 8.2 quake near Iquique were thankfully light thanks to the smallish tsunami and good Chilean building codes, the local fishing fleet was heavily damaged.  Iquique is mostly a mining town, and the port there is a mostly man made fill expanding on several rock islands just offshore.  In the lee of this port facility, were numerous small fishing boats that were trapped in the open ended roadstead when he tsunami arrived.  I doubt the local fishermen would call the damage light.

Wrecked boats in Iquique (AP photo)

This again reminded me of what would probably be a similar result to an earthquake of this size in the Pacific Northwest.  While we are well behind in preparedness, at least we know what to do.  Finding the will and the money is another matter.  But fishermen around the world are not so easily moved to higher ground, or at least their boats and livelihoods are not.  The same is true here in the northwest, in Japan, in Sumatra and wherever a subduction zone underlies the coast.  In first world countries, the answer is typically insurance, because there is no known cure for this problem. Well there is one cure, practiced in Japan, and that is massive tsunami walls and gates in some of the rivers and harbors. Elsewhere, not so much.

River gate in Minami-Sanriku (USGS)

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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