<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=iso-8859-1" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.18702">
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff><FONT size=2 face=Arial>
<DIV class=article-heading><FONT size=4>Canadian quake refines Pacific tsunami
risk</FONT></DIV></HGROUP>
<DIV>October 2012 tremor shifted the sea floor in unexpected ways.</DIV>
<DIV><SPAN class=vcard><A class=fn
href="http://www.nature.com/news/canadian-quake-refines-pacific-tsunami-risk-1.13234?WT.ec_id=NEWS-20130625#auth-1">Alexandra
Witze</A></SPAN></DIV>
<DIV class=pubdate-and-corrections><TIME datetime="2013-06-21" pubdate>Nature,
21 June 2013</TIME></DIV></HEADER><SECTION>
<DIV class="content no-heading cleared main-content">
<DIV class=video><A
href="http://www.nature.com/news/canadian-quake-refines-pacific-tsunami-risk-1.13234?WT.ec_id=NEWS-20130625">http://www.nature.com/news/canadian-quake-refines-pacific-tsunami-risk-1.13234?WT.ec_id=NEWS-20130625</A></DIV>
<DIV class=video> </DIV></DIV>
<DIV class="video-wrapper youtube video-full"><EM>Ocean motion. An animation of
tsunami waves propagating across the Pacific Ocean after a magnitude-7.7
earthquake struck the Haida Gwaii archipelago in British Columbia, Canada, in
2012. SOURCE: REF. 1</EM></DIV>
<DIV class="content no-heading cleared main-content"><ASIDE></DIV>
<DIV class=hidden>A study of the magnitude-7.7 earthquake that shook the
northern coast of British Columbia, Canada, last October has solved a
longstanding argument about the region’s geology. The finding suggests that even
Pacific islands as far away as Hawaii might need to worry about tsunamis
originating from this part of the Canadian coast.</DIV>
<DIV class="content no-heading cleared main-content">
<P>Most of the tsunami threat in North America's Pacific Northwest stems from
the Cascadia fault, where the Juan de Fuca crustal plate dives beneath
Washington, Oregon, and parts of California and British Columbia. The 2012 quake
struck north of that region, where the Pacific crustal plate slides towards
Alaska along a major geological fault known as the Queen Charlotte.</P>
<DIV style="WIDTH: 302px" class="img img-right">
<DIV
style="PADDING-BOTTOM: 1px; PADDING-LEFT: 1px; PADDING-RIGHT: 1px; PADDING-TOP: 1px"
class=img-content align=center><A class=lightbox-link
href="http://www.nature.com/news/quake-map-jpg-7.11157?article=1.13234"><IMG
class=lightbox alt=""
src="http://www.nature.com/polopoly_fs/7.11157.1371767745!/image/Quake-map.jpg_gen/derivatives/landscape_300/Quake-map.jpg"
data-derivative="fullsize" data-full-width="630"
data-full-height="1140"></A></DIV>
<DIV
style="PADDING-BOTTOM: 1px; PADDING-LEFT: 1px; PADDING-RIGHT: 1px; PADDING-TOP: 1px"
class=img-content> </DIV>
<DIV
style="PADDING-BOTTOM: 1px; PADDING-LEFT: 1px; PADDING-RIGHT: 1px; PADDING-TOP: 1px"
class=lightbox-icon><A class="lightbox-link hide-text" title=Expand
href="javascript:;">Expand</A></DIV>
<P
style="PADDING-BOTTOM: 1px; PADDING-LEFT: 1px; PADDING-RIGHT: 25px; PADDING-TOP: 1px"
class=credit>REF. 1</P></DIV>
<P>Many scientists had thought that this 'strike–slip' motion would not yield
big tsunamis, because the two sides of the sea floor move along the horizontal
axis, displacing less water than shifts upwards or downwards. But on 27 October
2012, the sea floor near the Haida Gwaii archipelago ruptured along a fault
perpendicular to the Queen Charlotte fault. The quake shoved a chunk of Pacific
sea floor directly under the North American continent, pushing it upwards and
creating the sort of vertical motion that can generate sizeable tsunamis (see
'Down and out').</P>
<P>Thorne Lay, a seismologist at the University of California, Santa Cruz, and
his colleagues describe this 'thrust' geometry in a paper published on 11 June
in <I>Earth and Planetary Science Letters</I><SUP><A id=ref-link-1
class=ref-link
title="Lay, T. et al. Earth Planet. Sci. Lett. http://dx.doi.org/10.1016/j.epsl.2013.05.005 (2013)."
href="http://www.nature.com/news/canadian-quake-refines-pacific-tsunami-risk-1.13234?WT.ec_id=NEWS-20130625#b1">1</A></SUP>.
The work confirms that big, dangerous quakes can happen in this region — an idea
suggested by researchers at the Geological Survey of Canada in the 1980s, but
one that had not been widely recognized, Lay says.</P>
<P>The earthquake was the second largest ever recorded in Canada by scientific
instruments. It sent tsunamis rushing at least 7.6 metres up the rugged and
sparsely populated western coast of Haida Gwaii. "If it had occurred in the
summer, there may well have been people in harm's way,” says Lucinda Leonard, a
geoscientist at the Geological Survey of Canada in Sidney, British Columbia, who
led a recent assessment of Canada's tsunami hazards<SUP><A id=ref-link-2
class=ref-link
title="Leonard, L. J., Rogers, G. C. & Mazzotti, S. A Preliminary Tsunami Hazard Assessment of the Canadian Coastline (Geological Survey of Canada, 2012); available at http://tinyurl.com/pbyy85d"
href="http://www.nature.com/news/canadian-quake-refines-pacific-tsunami-risk-1.13234?WT.ec_id=NEWS-20130625#b2">2</A></SUP>.</P>
<P>The quake also sent waves racing much farther afield. Forecasters sent alarms
to Hawaii, 4,000 kilometres away in the middle of the Pacific Ocean. Coastal
areas of several islands were evacuated, leading to huge traffic jams. And when
the tsunami that materialized was smaller than anticipated — no more than 80
centimetres — people were not impressed.</P>
<DIV class="related-stories-box box">"My friends on the north side of Oahu felt
like they'd been put in harm's way” in the rush to evacuate to higher ground,
says Lay. "We need to better anticipate when there will be dangerous
waves."</DIV>
<P>Lay thinks that the forecasters did the right thing by erring on the
conservative side and warning of a tsunami that was bigger than what actually
arrived. But next time, he says, they may do a better job, as they can plug data
from the Haida Gwaii quake into models and refine their predictions.</P>
<P>The Queen Charlotte fault itself is unlikely to break again in the near
future but geologists may need to rethink whether thrust faults near strike–slip
ones could break unexpectedly. The 1989 Loma Prieta quake, near San Francisco,
California, also had a surprising amount of vertical movement along a
strike–slip fault, says Lay.</P>
<P><A href="javascript:;" jQuery164035256287041074963="9"><STRONG><FONT
color=#000000>References</FONT></STRONG></A></P></DIV>
<DIV class=content><SPAN class="vcard author"><SPAN class=fn>Lay,
T.</SPAN></SPAN> <I>et al</I>. <SPAN class=source-title>Earth Planet. Sci.
Lett.</SPAN> <A
href="http://dx.doi.org/10.1016/j.epsl.2013.05.005">http://dx.doi.org/10.1016/j.epsl.2013.05.005</A>
(<SPAN class=year>2013</SPAN>). <A class="context-link show"
href="javascript:;">Show context</A> </DIV>
<DIV class=content><SPAN class="vcard author"><SPAN class=fn>Leonard, L.
J.</SPAN></SPAN>, <SPAN class="vcard author"><SPAN class=fn>Rogers, G.
C.</SPAN></SPAN> & <SPAN class="vcard author"><SPAN class=fn>Mazzotti,
S.</SPAN></SPAN> <SPAN class=book-title>A Preliminary Tsunami Hazard Assessment
of the Canadian Coastline</SPAN> (Geological Survey of Canada, 2012); available
at <A href="http://tinyurl.com/pbyy85d">http://tinyurl.com/pbyy85d</A> <A
class="context-link show" href="javascript:;">Show context</A></DIV>
<DIV class=content> </DIV>
<DIV class=content> </DIV></SECTION><SECTION>
<DIV class="section-heading toggle"><A href="javascript:;"
jQuery164035256287041074963="10"><FONT color=#000000><STRONG>Related stories
and</STRONG> <STRONG>links</STRONG></FONT></A><U> <STRONG>from
nature.com</STRONG></U></DIV>
<DIV class=content><ARTICLE></DIV>
<DIV><A href="http://www.nature.com/doifinder/10.1038/476391a">Earthquakes from
the ocean: Danger zones</A> <SPAN class=time>24 August
2011</SPAN></TIME></DIV>
<DIV><A href="http://www.nature.com/doifinder/10.1038/news.2010.270">Risk of
giant quake off American west coast goes up</A> <SPAN class=time>31 May
2010</SPAN></TIME></DIV>
<DIV><A href="http://www.nature.com/doifinder/10.1038/news031124-2">American
super-quake caused Japanese deluge</A> <SPAN class=time>25 November
2003</SPAN></TIME></DIV>
<DIV></ARTICLE></DIV></FONT></BODY></HTML>