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<!-- span class="title">SeisComP Release</span -->
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<span class="version">6.9.1</span>
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<section id="mb">
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<span id="global-mb"></span><h1>mb<a class="headerlink" href="#mb" title="Permalink to this heading">¶</a></h1>
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<p>Body wave magnitude at teleseismic distances</p>
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<section id="description">
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<h2>Description<a class="headerlink" href="#description" title="Permalink to this heading">¶</a></h2>
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<p>mb is the standard body-wave magnitude.
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Compare also with the <a class="reference internal" href="global_mb_bb.html#global-mb-bb"><span class="std std-ref">mB magnitude</span></a>.</p>
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<section id="amplitude">
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<h3>Amplitude<a class="headerlink" href="#amplitude" title="Permalink to this heading">¶</a></h3>
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<p>mb is defined on the amplitude of the first few cycles of the P-wave,
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typically a time window of 20 s - 30 s. Only the first few cycles are used to
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minimize the effects of radiation pattern and depth phases, which result in
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complicate waveform signatures.
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In <cite>SeisComP</cite> mb amplitudes are measured on vertical-component displacement seismograms
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in a 30 s time window after simulation of a <a class="reference internal" href="../base/glossary.html#term-WWSSN_SP"><span class="xref std std-term">WWSSN_SP</span></a> short-period
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seismometer. Amplitudes are used from stations with epicentral distances between
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5° and 105° (configurable). The methods for measuring amplitudes are configurable
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in the global bindings.</p>
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</section>
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<section id="station-magnitude">
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<h3>Station Magnitude<a class="headerlink" href="#station-magnitude" title="Permalink to this heading">¶</a></h3>
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<p>The general formula is</p>
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<div class="math">
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<p><img src="../_images/math/557ff47b5e6e082cc7dd08a231e296efbdf54331.png" alt="mb = \log \left(\frac{A}{T}\right) + Q(h,\Delta) - 3.0"/></p>
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</div><p>with A as the displacement amplitude in micrometers, T as the dominant period of
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the signal in seconds, Q as a correction term for depth and distance. mb is
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usually determined at periods around 1s in adaptation to the use
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of the World-Wide Standard Seismograph Network (WWSSN) short-period stations.
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A scatter in the order of +/- 0.3 for the station magnitudes is usual.
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Typically, mb is determined for stations with distances larger than 5° to
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have a distinct direct P-wave phase. A correction term for the distance has to
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be determined empirically, which is quite complicate for distances smaller than 20°.
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This reflects the complexity of the body waves that traverse only in the upper
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mantle. mb saturates at about magnitude 5.5 to 6.0 because the maximum amplitudes of larger
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earthquakes occur at lower frequencies than the frequency range between 0.7 Hz - 2 Hz
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used for the magnitude calculation.</p>
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<ul class="simple">
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<li><p>Amplitude unit in <cite>SeisComP</cite>: <strong>nanometers</strong> (nm)</p></li>
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<li><p>Time window: 30 s</p></li>
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<li><p>Default distance range: 5 - 105 deg, configurable: <a class="reference internal" href="global.html#confval-magnitudes.mb.minDist"><code class="xref std std-confval docutils literal notranslate"><span class="pre">magnitudes.mb.minDist</span></code></a>,
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<a class="reference internal" href="global.html#confval-magnitudes.mb.maxDist"><code class="xref std std-confval docutils literal notranslate"><span class="pre">magnitudes.mb.maxDist</span></code></a></p></li>
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<li><p>Depth range: no limitation, for depth < 0 km, depth = 0 km is assumed</p></li>
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</ul>
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<div class="admonition note">
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<p class="admonition-title">Note</p>
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<p>In 2013 the IASPEI commission (<span id="id1">IASPEI [<a class="reference internal" href="../base/references.html#id40" title="IASPEI. Summary of magnitude working group recommendations on standard procedures for determining earthquake magnitudes from digital data. IASPEI Website, 2013. URL: http://www.iaspei.org/commissions/commission-on-seismological-observation-and-interpretation/Summary_WG_recommendations_20130327.pdf.">46</a>]</span>) recommended a minimum distance of
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20 deg. However, <a class="reference internal" href="scautoloc.html#scautoloc"><span class="std std-ref">scautoloc</span></a> requires mb amplitudes by default for
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considering a pick.
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For maintaining consistency, 5 deg is therefore kept as the default
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for <a class="reference internal" href="global.html#confval-magnitudes.mb.minDist"><code class="xref std std-confval docutils literal notranslate"><span class="pre">magnitudes.mb.minDist</span></code></a>.</p>
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</div>
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</section>
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<section id="network-magnitude">
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<h3>Network magnitude<a class="headerlink" href="#network-magnitude" title="Permalink to this heading">¶</a></h3>
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<p>By default, the trimmed mean is calculated from the station magnitudes to form
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the <a class="reference internal" href="../base/glossary.html#term-network-magnitude"><span class="xref std std-term">network magnitude</span></a>. Outliers beyond the outer 12.5% percentiles are
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removed before forming the mean.</p>
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</section>
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<section id="configuration">
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<h3>Configuration<a class="headerlink" href="#configuration" title="Permalink to this heading">¶</a></h3>
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<p>Adjust the configurable parameters in global bindings in the mB section or use
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<code class="file docutils literal notranslate"><span class="pre">global.cfg</span></code>
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as in <a class="reference internal" href="global_mlv.html#global-mlv"><span class="std std-ref">MLv</span></a>. Add mb to the list of computed amplitudes and magnitudes
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in the configuration of
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<a class="reference internal" href="scamp.html#scamp"><span class="std std-ref">scamp</span></a> and <a class="reference internal" href="scmag.html#scmag"><span class="std std-ref">scmag</span></a> and in <a class="reference internal" href="scesv.html#scesv"><span class="std std-ref">scesv</span></a> or <a class="reference internal" href="scolv.html#scolv"><span class="std std-ref">scolv</span></a>/<a class="reference internal" href="scesv.html#scesv"><span class="std std-ref">scesv</span></a>
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for visibility.</p>
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<h3><a href="../index.html">Table of Contents</a></h3>
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<ul>
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<li><a class="reference internal" href="#">mb</a><ul>
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<li><a class="reference internal" href="#description">Description</a><ul>
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<li><a class="reference internal" href="#amplitude">Amplitude</a></li>
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<li><a class="reference internal" href="#station-magnitude">Station Magnitude</a></li>
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<li><a class="reference internal" href="#network-magnitude">Network magnitude</a></li>
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<li><a class="reference internal" href="#configuration">Configuration</a></li>
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