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- I placed a moment tensor \/ focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors<\/a> and focal mechanisms<\/a> (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor shows northeast-southwest compression, perpendicular to the convergence at this plate boundary. Most of the recent seismicity in this region is associated with convergence along the New Britain trench or the South Solomon trench. <\/li>\n
- I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here<\/a> and here<\/a>. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.<\/li>\n
- I include the slab contours plotted (Hayes et al., 2012<\/a>), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this close to the location of the fault as mapped by Hayes et al. (2012). The M 6.8 is plotted really close to the megathrust and is also very shallow. The depth is probably not very well constrained due to the geometry and lack of seismometer coverage in the oceanic setting.<\/li>\n<\/ul>\n
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- Here is the USGS page for the main earthquake in this sequence.<\/strong><\/li>\n
- 2017.10.31 M 6.8<\/a><\/li>\n<\/ul>\n
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I include some inset figures.<\/strong><\/h3>\n<\/li>\n
- In the upper left corner I include a figure from Richards et al. (2011) that shows the major plate boundary faults in the region. They also plot seismicity with color representing depth. This allows us to visualize the subduction zone fault as it dips (eastward for the New Hebrides and westwards for the Tonga subduction zones). The cross section in the panel on the right is designated by the black dashed line. I also place this line as a dashed green line in the interpretive poster below. I place a yellow star in the general location of the M 6.8 earthquake.<\/li>\n
- In the upper right corner I include the Richards et al. (2011) cross section showing earthquake hypocenters as colored circles and the megathrust subduction zone faults as red lines.<\/li>\n
- To the left of the cross section is a panel that shows how Richards et al. (2011) hypothesize about how the New Hebrides subducting slab (Australia plate) and the Fiji Basin (the upper plate) interacted to create the configuration of the plates and faults in this region. Note how shallow the New Hebrides fault is.<\/li>\n
- In the lower left corner I plot the USGS moment tensors for the main earthquakes from this sequence. Note how the mainshock is a thrust (compressional) earthquake, while the earthquakes in the downgoing Australia plate, to the west of the subduction zone, are mostly normal (extensional) earthquakes. There are many examples of this globally (Samoa, Marianas, Kuril, etc.). I will follow up by linking other reports of mine that discuss these at a later time. I am working on very little sleep from my travels.<\/li>\n<\/ul>\n
\n![\"\"](\"http:\/\/earthjay.com\/earthquakes\/20171031_new_caledonia\/20171031_new_caledonia_interpretation.jpg\")
<\/a><\/p>\n- \n
- Here is my interpretive poster for the 2016.12.08 earthquake.<\/li>\n
\n![\"\"](\"http:\/\/earthjay.com\/earthquakes\/20161208_solomon\/20161208_solomon_interpretation.jpg\")
<\/a><\/ul>\n- \n
- Here is an animation that shows the seismicity for this region from 1960 – 2016 for earthquakes with magnitudes greater than or equal to 7.0. <\/li>\n
- I include some figures mentioned in my report from 2016.04.28<\/a> for a sequence of earthquakes in the same region as today’s earthquake (albeit shallower hypocentral depths), in addition to a plot from Cleveland et al. (2014). In the upper right corner, Cleveland et al. (2014) on the left plot a map showing earthquake epicenters for the time period listed below the plot on the right. On the right is a plot of earthquakes (diameter = magnitude) of earthquakes with latitude on the vertical axis and time on the horizontal axis. Cleveland et al (2014) discuss these short periods of seismicity that span a certain range of fault length along the New Hebrides Trench in this area. Above is a screen shot image and below is the video.<\/li>\n
\n![\"\"](\"http:\/\/earthjay.com\/earthquakes\/20160406_vanuatu\/1960_2016_vanuatu_EQ_GTE_70_10yr.JPG\")
<\/a><\/p>\n- Here is a link<\/a> to the embedded video below (6 MB mp4)<\/li>\n
\n - Here is a link<\/a> to the embedded video below (6 MB mp4)<\/li>\n
- 2017.10.31 M 6.8<\/a><\/li>\n<\/ul>\n
- I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here<\/a> and here<\/a>. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.<\/li>\n