Elements of Seismology Lecture Notes PDF

04/09/2023 SEISMOLOGY...

04/09/2023 SEISMOLOGY It is the scientific study of earthquakes and the propagation of elastic waves through the Earth. The field also includes studies of earthquake environmental effects z ELEMENTS OF such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes SEISMOLOGY such as explosions. A related field that uses geology to infer information regarding past earthquakes is paleoseismology. CE163-1 EARTHQUAKE ENGINEERING ENGR. NESLYN L. PRINCIPIO, MSCE 1 2 ELEMENTS OF ENGINEERING SEISMOLOGY 1. Studying earthquake history and tectonics to assess the Engineering seismology is the study and application of seismology earthquakes that could occur in a region and their characteristics for engineering purposes. It generally applied to the branch of and frequency of occurrence. seismology that deals with the assessment of the seismic hazard of a 2. Studying strong ground motions generated by earthquakes to assess the expected shaking from future earthquakes with similar site or region for the purposes of earthquake engineering. characteristics. These strong ground motions could either be observations from accelerometers or seismometers or those simulated by computers using various techniques. 3 4  04/09/2023 The theory of plate tectonics derives from the theory of continental drift and floor spreading. Image Reference: https://i.imgur.com/62X3ME4.gif 5 6 - crust part and the rigid uppermost part of the mantle low viscosity, shear strength and can flow like liquid on the geographical times scales 7 8  04/09/2023 This sudden slip, termed Elastic Rebound by Reid (1910) based on his studies of regional deformation following the 1906 San Francisco Earthquake, releases large amounts of energy, which constitutes or is the earthquake. 9 10 z PLATE BOUNDARIES MOVEMENT The lateral movement of the plates is mainly at the speeds of 50-100 mm annually. Earthquakes, volcanoes, mountain and oceanic trench formation normally occur along these boundaries. 11 12  04/09/2023 D C I O V N E V R E G R E G N E T N T https://thumbs.gfycat.com/ConsciousGivingEyelashpitviper-small.gif https://thumbs.gfycat.com/UnknownThinFishingcat-size_restricted.gif 13 14 T R A N S F O R M This refers to the plunging of one plate (e.g., the Pacific) beneath another, into the mantle, due to convergent motion Typically characterized by volcanism, as a portion of the plate (melting in the lower mantle) remerges as volcanic lava https://thumbs.gfycat.com/GentleLegalGull-size_restricted.gif https://media2.giphy.com/media/fnZxMhYy7zuqvsLG4J/200_d.gif 15 16  04/09/2023 Subduction occurs along the following:  west coast of South America at the boundary of the Nazca and South American Plate  Central z America (boundary of the Cocos and Caribbean plates),  Taiwan and Japan (boundary of the Philippines and Eurasian plates),  North American Pacific Northwest (boundary of the Juan de Fuca and North American Plates) Stretching 40,000 km (24,000 miles) around the circumference of the Pacific Ocean Plates that make up the Pacific basin are generally subducting beneath continental plates, causing subduction-zones volcanism in the surface.. Nearly 80% of the earth’s volcanoes are found near the tectonic plate boundaries of the Pacific Ocean. 17 18 z FAULTING  A FAULT is a zone of the earth’s crust within which the two sides have moved. Faults may be hundreds of miles long, from one to over one hundred miles deep, and are sometimes not readily apparent on the ground zone. Tectonic Plates move relatively slowly (5 cm per year is relatively fast) and irregularly, with relatively frequent small and only occasional large earthquakes. violent motions produce the shaking that is felt as an earthquake https://37.media.tumblr.com/49eaaa37bb599b85c8c3bec815b6a21b/tumblr_n7qq998svs1qio57co1_500.gif 19 20  04/09/2023 z z TYPES OF EARTHQUAKE FAULT: TYPES OF EARTHQUAKE FAULT: Strike-slip Fault Normal Fault A dip-slip fault in which the block above the fault has A fault on which the two blocks slide past one another. moved downward relative to the block below. The San Andreas Fault is an example of right lateral observed in the Western United States Basin and Range fault. Province and along oceanic ridge system. https://thumbs.gfycat.com/MiserablePerfumedFlee-size_restricted.gif https://media0.giphy.com/media/1zgOYLsKZpj2cONhdZ/200w.gif 21 22 z TYPES OF EARTHQUAKE FAULT: Thrust or Reverse Fault A dip-slip fault in which the upper block, above the fault plane, moves up and over the lower block. Common in areas of compression, such as regions where one plate is being subducted under another as Japan. https://thumbs.gfycat.com/BabyishRipeAzurevasesponge-size_restricted.gif 23 24  04/09/2023 Generally, earthquakes will be concentrated in the vicinity of faults. Faults that are moving more rapidly than others will tend to have a higher rates of seismicity, Larger faults are more likely to produce a large events than others. However, earthquakes continue to occur on "unknown" or "inactive" faults. Oblique-slip fault - a fault in which the displacements of the strike-slip and dip-slip components have very similar magnitudes; fault movement occurs obliquely across the fault surface. 25 26 several earthquakes in the 1980's, none of which were accompanied by surface faulting (Stein and Yeats 1989). Youtube link for other visualization of Plate tectonics: https://www.youtube.com/watch?v=RA2-Vc4PIOY Next Topic: Propagation of Seismic Disturbances z Blind Thrust Faults end. - Hidden - associated with folded topography in general, including areas of lower and infrequent seismicity - potential for an earthquake exists in any area even if there are few or no earthquakes in the historic record. 27 28