{"id":208,"date":"2015-04-07T17:19:01","date_gmt":"2015-04-07T08:19:01","guid":{"rendered":"http:\/\/www.eri.u-tokyo.ac.jp\/_html\/en\/?p=208"},"modified":"2016-04-14T16:47:31","modified_gmt":"2016-04-14T07:47:31","slug":"a-100-m-fabry-perot-cavity-with-automatic-alignment-controls-for-long-term-observations-of-earths-strain","status":"publish","type":"post","link":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/research\/208\/","title":{"rendered":"A 100-m Fabry\u2013P\u00e9rot Cavity with Automatic Alignment Controls for Long-Term Observations of Earth\u2019s Strain"},"content":{"rendered":"<p style=\"text-align: center;\">Akiteru Takamori, Akito Araya, Wataru Morii, Souichi Telada, Takashi Uchiyama and Masatake Ohashi<\/p>\n<p style=\"text-align: center;\">\n<p style=\"text-align: center;\">Technologies 2014, 2(3), 129-142; doi:10.3390\/technologies2030129<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Abstract<\/strong>: We have developed and built a highly accurate laser strainmeter for geophysical observations. It features the precise length measurement of a 100-m optical cavity with reference to a stable quantum standard. Unlike conventional laser strainmeters based on simple Michelson interferometers that require uninterrupted fringe counting to track the evolution of ground deformations, this instrument is able to determine the absolute length of a cavity at any given time. The instrument offers advantage in covering a variety of geophysical events, ranging from instantaneous earthquakes to crustal deformations associated with tectonic strain changes that persist over time. An automatic alignment control and an autonomous relocking system have been developed to realize stable performance and maximize observation times. It was installed in a deep underground site at the Kamioka mine in Japan, and an effective resolution of 2 \u00d7 (10\u22128 \u2212 10\u22127) m was achieved. The regular tidal deformations and co-seismic strain changes were in good agreement with those from a theoretical model and a co-located conventional laser strainmeter. Only the new instrument was able to record large strain steps caused by a nearby large earthquake because of its capability of absolute length determination.<\/p>\n<figure id=\"attachment_1469\" aria-describedby=\"caption-attachment-1469\" style=\"width: 300px\" class=\"wp-caption alignnone\"><a href=\"http:\/\/www.eri.u-tokyo.ac.jp\/old\/en\/wp-content\/uploads\/sites\/3\/2015\/04\/20150219_fig1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1469 size-medium\" src=\"http:\/\/www.eri.u-tokyo.ac.jp\/old\/en\/wp-content\/uploads\/sites\/3\/2015\/04\/20150219_fig1-300x225.png\" alt=\"In Kamioka \" width=\"300\" height=\"225\" \/><\/a><figcaption id=\"caption-attachment-1469\" class=\"wp-caption-text\">Laser strainmeter located in Kamioka<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Akiteru Takamori, Akito Araya, Wataru Morii, Souichi Telada, Takashi Uchiyama and Masatake Ohashi Technologies &hellip; <a href=\"https:\/\/www.eri.u-tokyo.ac.jp\/en\/research\/208\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;A 100-m Fabry\u2013P\u00e9rot Cavity with Automatic Alignment Controls for Long-Term Observations of Earth\u2019s Strain&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"class_list":["post-208","post","type-post","status-publish","format-standard","hentry","category-research"],"_links":{"self":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/208"}],"collection":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/comments?post=208"}],"version-history":[{"count":1,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/208\/revisions"}],"predecessor-version":[{"id":209,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/208\/revisions\/209"}],"wp:attachment":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/media?parent=208"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/categories?post=208"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/tags?post=208"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}