Seismic Wave Crackers 6 Pc
Nerio Cintron
Because earthquakes can cause walls to crack, foundations to move and even entire buildings to crumple, engineers incorporate into their structural designs techniques that withstand damage from earthquake forces, for example, cross bracing, large bases and tapered geometry. Earthquake-proof buildings are intended to bend and sway with the motion of earthquakes, or are isolated from the movement by sliders. Engineers use the engineering design process to come up with an idea, test it, and then re-engineer the structure based on its performance.
Explain that engineers ask critical questions about what they want to create or what specific problem they are trying to solve. These questions include: What are the project requirements (criteria)? What are the limitations (constraints)? This also requires conducting research on the problem. For example, civil engineers work together with scientists, as well as engineers from different backgrounds, to better understand the problem of how to design earthquake-proof buildings.
The engineering team then imagines possible solutions to the problem. This takes a lot of creative brainstorming! After making a list of solutions and some sketches of their ideas, the team of engineers plan and select their best idea.
Once the team decides on the details of the final design, they create the prototype and test it out! Prototypes are smaller models that are used by engineers to test a design. In the testing phase, the team pays attention to what needs to be changed to the model to make the product work better. The last step of the engineering design process is to improve (iterate) their design.
Discussion: Discuss with students how natural processes create earthquake hazards. Teachers can also use the Earthquakes Rock! lesson to demonstrate how earthquakes cause waves of movement in the ground.
Before/After: Have students list types of changes they expect to see in their structures before they test them, then illustrate changes in their structures, after they complete the simulations. Ask students to identify one variable and discuss what happened when they changed the variable. They could reflect on these changes and their causes in a post-activity science journal entry.
As another option, show students before and after pictures of earthquake damage, comparing buildings which remained standing with the least damage to those which did not survive. Students could discuss possible reasons for the damage, observing structure (height, etc.) of the buildings.
Inform students that in an experimental testing lab or during science experiments, nothing should ever be put into their mouths. The marshmallows and Jell-O are not for consumption. Instead, set some aside for a treat after the activity.
Research how to obtain fault maps of the area. The U.S. Geological Survey ( ) or the Federal Emergency Management Agency ( ) are good places to search. Is the area in a zone at risk for earthquakes? Do local building codes and architecture plan for this?
Students learn about the types of seismic waves produced by earthquakes and how they move through the Earth. Students learn how engineers build shake tables that simulate the ground motions of the Earth caused by seismic waves in order to test the seismic performance of buildings.
Students learn about tsunamis, discovering what causes them and what makes them so dangerous. They learn that engineers design detection and warning equipment, as well as structures that that can survive the strong wave forces. In a hands-on activity, students use a table-top-sized tsunami generator...
The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education, and National Science Foundation (GK-12 grant no 0338326). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.
Foods are often used to demonstrate how Earth is made of four main layers, metaphors that call to mind a tasty snack: graham crackers for the crust, ice cream for the mantle, melted marshmallows for the outer core and chocolate chips for the inner core.
The team behind the latest research probed Earth's center in an innovative way using three earthquake datasets, each of which saw the core differently, study co-author Hrvoje Tkalčić told Space.com in an email. One of the events they studied was the 7.9-magnitude earthquake that occurred in 2017 in the Solomon Islands.
"Earth oscillates like a bell after a large earthquake, and not just for hours, but days," Hrvoje Tkalčić, a geophysicist at the Australian National University and co-author of the latest study, said in a statement.
So the team combined seismic data recorded by different data centers worldwide about the large earthquake in the Solomon Islands, and studied a type of seismic wave called the primary, pressure or P wave. The P wave is the fastest of all seismic waves and the only one that passes through Earth's center, so studying it as it crossed Earth's center five times illuminated the planet's deep interior.
Tkalčić's team found that the wave took 20 minutes to travel the planet's width. Each time it did so, they saw the innermost core's "anisotropic" property on clear display: Seismic waves passing through the innermost inner core slowed in one direction while those moving through the outer layer slowed in a different direction.
Scientists knew as early as 2003 that the innermost inner core is anisotropic, so the latest research strengthens that knowledge with clearer evidence. In the new study, researchers found that the direction of P waves inside the innermost core is slowest at an "oblique" angle with the equatorial plane, or 50 degrees from Earth's rotation axis.
There is strong evidence that slow-moving iron in Earth's core powers the planet's geodynamo, which leads to generation of the Earth's global magnetic field. So understanding what's happening at the planet's very center will shed light on how the magnetic field behaves and at times reverses.
Significant additional effects were felt worldwide in the days and weeks after the volcano's eruption. Additional seismic activity was reported until February 1884, but any reports after October 1883 were dismissed by Rogier Verbeek's subsequent investigation into the eruption.
In the years before the 1883 eruption, seismic activity around the Krakatoa volcano was intense, with earthquakes felt as far away as North Australia, one of which, in 1880, damaged a lighthouse.[4] Strombolian activity began on 20 May 1883, and steam venting began to occur regularly from Perboewatan, the northernmost of the island's three cones. Eruptions of ash reached an estimated altitude of 6 km (20,000 ft), and explosions could be heard in Batavia (Jakarta) 160 km (100 mi) away, rattling windows and doors.[5][4] Dust fell 300 miles away. An excursion party sent to the island on 26 May reported that the islands were covered with a fine white dust, with explosions coming from Perboewatan every 5 to 10 minutes. Although by this time the eruptions were calming down, some of the explosions were still very energetic, hurling pumice opposite the direction of the wind. A large crater about 3,000 feet (900 metres) in diameter formed, with a cavity from which issued plumes of steam. The eruptions soon quietened after the initial violence.[4]
Around 16 June, there were loud explosions and a thick black cloud covered the islands for five days. The eruptions started gaining strength again on 19 June. On 24 June, a prevailing east wind cleared the cloud, and two ash columns could be seen issuing from Krakatoa. It was also noticed that the summit cone of Perboewatan was gone, which an extensive report of a few years later attributes it to having been blown away. The seat of the eruption is believed to have been a new vent or vents that formed on that day, between Perboewatan and Danan. The violence of the ongoing eruptions caused tides in the vicinity to be unusually high, and ships at anchor had to be moored with chains. Earthquakes were felt at Anyer, Banten, and ships began to report large pumice masses to the west in the Indian Ocean.[5][4] A third vent, and later many more, appeared. The eruptions continued throughout July, and their violence continued to increase until the explosions of 27 August.[4]
In early August, a Dutch topographical engineer, Captain H. J. G. Ferzenaar, investigated the Krakatoa islands.[5] He noted three major ash columns (the newer from Danan), which obscured the western part of the island, and steam plumes from at least eleven other vents, mostly between Danan and Rakata. When he landed, he noted an ash layer about 0.5 m (1 ft 8 in) thick and the destruction of all vegetation, leaving only tree stumps. He advised against any further landings.[5]
By 25 August, the Krakatoa eruptions intensified. At about 1:00 pm on 26 August, the volcano entered its paroxysmal phase. By 2:00 pm, a black ash cloud could be seen 27 km (17 mi) high. At this point, the eruption was almost continuous, and explosions could be heard every ten minutes. By 5:00 pm, the explosions were audible all over Java. Waves a few feet in height began battering the coasts of Java and Sumatra at 5:30 pm, and continued throughout the night, which may have been produced by steam explosions. [4] Ships within 20 km (12 mi) of the volcano reported heavy ash fall, with pieces of hot pumice up to 10 cm (4 in) in diameter landing on their decks. Between 7:00 pm and 8:00 pm, a small tsunami hit the shores of Java and Sumatra, 40 km (25 mi) away.
Massive tsunamis struck the coastlines of the Sunda Strait, entirely submerging some islands.[13] The tsunamis produced by the third explosion were the largest, although the first two explosions did produce smaller tsunamis.[14] The waves reached heights of up to 24 metres (79 feet) along the south coast of Sumatra and up to 42 metres (138 feet) along the west coast of Java.[15] The Loudon, which at the time was anchored near the village of Telok Betong, survived the waves. Passengers produced this eyewitness account:[16]
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