This M 6.8 earthquake happened in the Atlas Mountains, a compressional system with south dipping reverse faults on the north and north dipping reverse faults on the south.<\/p>\n
It is possible, if not probable, that this earthquake is related to one of these reverse faults. Based on the location, it seems possible that this earthquake is on a south dipping thrust fault (associated with the North Atlas fault system).<\/p>\n
I used the USGS earthquake catalog and it appears that this is the largest magnitude earthquake to happen in Morocco (since we started recording earthquakes on seismometers). <\/p>\n
Here is the sobering part of this earthquake. The USGS PAGER Alert provides an estimate for the number of casualties and economic impact. Read more about how these estimates are produced (and how to read this report) here<\/a>.<\/p>\n UPDATE: (2023.09.10 Version 7) UPDATE: (2023.09.11) Empirical fault scaling relations are ways that we can compare fault rupture sizes with earthquake magnitudes. One of the most used and well cited empirical fault scaling relations paper is Wells and Coppersmith, 1994.<\/p>\n Here is the USGS fault slip model for the M 6.8 earthquake. The length of the fault slip figure is about 40 kilometers (km) and the width of the fault is about 45 km. The color represents the amount that the fault slipped (in meters) during the earthquake. So, the slip area does not fill this entire area. Most of the slip length is within ~30 km and width is within ~35km. The maximum slip is ~1.7 meters.<\/p>\n Here is a plot from Wells and Coppersmith that shows the data relating magnitude with subsurface rupture length. We can see that there is a positive relation between magnitude and length (as the length is larger, so is the magnitude).<\/p>\n \n(a) Regression of subsurface rupture length on magnitude (M). Regression line shown for all-slip-type relationship. Short dashed line indicates 95% confidence interval. (b) Regression lines for strike-slip relationships. See So, I used these scaling relations to calculate the magnitude for earthquakes of varying subsurface fault length. Here is a table from those calculations.<\/p>\n aftershocks may last for weeks, possibly months. aftershocks typically decay at a rate that is dependent on the fault system. each fault system is slightly different.<\/p>\n Here is a short story about aftershocks<\/a> in Northern California but this story is relevant to earthquakes elsewhere.<\/p>\n we don’t know the specific rate of decay for a fault system until we observe the aftershocks decay for that fault. some faults have few aftershocks and others have robust aftershock sequences (many events).<\/p>\n it is not satisfying to not know how long they will last, i understand.<\/p>\n e.g., there was an earthquake in central Washington USA in 1872<\/a> and some argue that this continues to have aftershocks.<\/p>\n so, they will last a while and nobody will know when they will stop. <\/p>\n but for people to feel safe to start living in their homes again, they need to get an expert, like an engineer, to evaluate the stability of their houses. only an expert, who is trained to inspect structures, can make these evaluations.<\/p>\n will there be other large earthquakes?<\/strong> this is something nobody can know.<\/p>\n follow advice for getting an engineer to check out one’s building(s) so that they can feel safe living in them; if the engineer decides that the structure is safe to withstand earthquakes, that is the best we can do.<\/p>\n the M6.8 changed the stresses in the crust adjacent to the earthquake. in some places, these stresses increased the chance for earthquakes on different (or the same) faults. in other places, they decreased the stress.<\/p>\n these changes in stress are modest but can trigger a new earthquake. but this depends on the state of stress of the other earthquake fault, something that we cannot yet know. so, we cannot know if the places where stress is increased will have a triggered\/new earthquake.<\/p>\n the best we can do is to make sure that buildings are resistant to earthquake forces. this capability is reliant on engineers, building inspectors, competent building contractors, building codes, etc. AND that these people follow the rules (building codes).<\/p>\n the Feb 2023 T\u00fcrkiye earthquakes destroyed buildings that were constructed under well designed building codes. but they were destroyed because people did not follow the code. lots of buildings were built before the codes existed and those did not perform well either.<\/p>\n so, when living in earthquake country, one simply needs to ensure that they are living\/working in earthquake resistant buildings. they may find comfort to live outside these structures until they are inspected. this is the smart thing to do.<\/p>\n i don’t have the expertise to know if a building is designed to withstand earthquakes. i am not a structural engineer, an earthquake engineer. i know some and can follow the local building codes here where i live. and i sure could not offer advice remotely. one simply needs to seek local expertise. i wish i could offer more advice.<\/p>\n finally, people who have been traumatized by this earthquake and continue to be traumatized by these aftershocks are going through what everyone does when faced with these conditions. this is typical. maybe finding comfort with friends and family and neighbors will help (?).<\/p>\n i hope i have provided some constructive feedback to your questions\/concerns.<\/p>\n hopefully this information can help those in Morocco cope with this extremely challenging natural hazard.<\/p>\n if nothing else, the survivors will be able to build back stronger and more earthquake resistant.<\/p>\n<\/ul>\n FOS = Resisting Force \/ Driving Force<\/strong><\/p>\n<\/li>\n Learning Resource: Sentinel-1 Synthetic Aperture Radar Interferometric Coherence Image Services StoryMap<\/p>\n This StoryMap tutorial enhances access to the Global Seasonal Sentinel-1 Interferometric Coherence and Backscatter dataset with image services. #SAR<\/a> https:\/\/t.co\/VjghtQiBUL<\/a> pic.twitter.com\/zMNLwuAdi3<\/a><\/p>\n — NASAEarthdata (@NASAEarthData) September 11, 2023<\/a><\/p><\/blockquote>\n
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\n![\"\"](\"https:\/\/earthjay.com\/earthquakes\/20230908_morocco\/20230908_morocco_68_onepager_14.jpg\")
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\nFault Scaling Relations<\/font><\/H3><\/p>\n
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\n![\"\"](\"https:\/\/earthjay.com\/earthquakes\/20230908_morocco\/20230908_morocco_68_slip_02.png\")
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\n![\"\"](\"https:\/\/earthjay.com\/earthquakes\/20230908_morocco\/wells_coppersmith_1994_fig_14.jpg\")
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\nTable 2 for regression coefficients. Length of regression lines shows the range of data for each relation.\n<\/p><\/blockquote>\n
\n![\"\"](\"https:\/\/earthjay.com\/earthquakes\/20230908_morocco\/20230908_morocco_wells_coppersmith_subsurface.jpg\")
<\/a><\/p>\nBelow is my interpretive poster for this earthquake<\/font><\/H2><\/p>\n
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I include some inset figures. Some of the same figures are located in different places on the larger scale map below.<\/font><\/H3><\/p>\n
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\n![\"\"](\"https:\/\/earthjay.com\/earthquakes\/20230908_morocco\/20230908_morocco_interpretation_20230910.jpg\")
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\n![\"\"](\"https:\/\/earthjay.com\/earthquakes\/20230908_morocco\/20230908_morocco_interpretation_20230912.jpg\")
<\/a>\n<\/ul>\nOther Report Pages<\/font><\/strong><\/H2><\/p>\n
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Discussion about aftershocks<\/font><\/strong><\/h2>\n
\nthe following is a series of statements that i wrote to respond to someone who is in Morocco<\/a>. i thought that perhaps others might find this useful. <\/p>\n
Shaking Intensity<\/font><\/strong><\/h2>\n
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\n![\"\"](\"https:\/\/earthjay.com\/earthquakes\/20230908_morocco\/20230908_morocco_intensity_interpretation_20230911.jpg\")
<\/a><\/p>\n<\/ul>\nPotential for Ground Failure<\/font><\/strong><\/h2>\n
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\nThere are many different ways in which a landslide can be triggered. The first order relations behind slope failure (landslides) is that the \u201cresisting\u201d forces that are preventing slope failure (e.g. the strength of the bedrock or soil) are overcome by the \u201cdriving\u201d forces that are pushing this land downwards (e.g. gravity). The ratio of resisting forces to driving forces is called the Factor of Safety (FOS). We can write this ratio like this:<\/p>\n
\n![\"\"](\"http:\/\/earthjay.com\/earthquakes\/20180928_indonesia\/force_balance_landscape.jpg\")
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\n![\"\"](\"http:\/\/earthjay.com\/earthquakes\/20180928_indonesia\/liquefaction_pore_pressure_change_patton.jpg\")
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\n![\"\"](\"http:\/\/earthjay.com\/earthquakes\/20180928_indonesia\/landslide_terminology_patton.jpg\")
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\n![\"\"](\"https:\/\/earthjay.com\/earthquakes\/20230908_morocco\/20230908_morocco_ground_failure_interpretation_20230911.jpg\")
<\/a><\/p>\n<\/ul>\nRemote Sensing of Surface Deformation<\/font><\/strong><\/h2>\n
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