Earthquakes, hurricanes, floods and droughts: where and why

Grade 9 Social Studies Worksheet

Circle the best answer.

1. Read this first

   Card A, plate map of Region Ardmoor (an invented region, made up for practice)

   a plate edge runs along the coast for 600 km, then turns inland and runs through the Veld Mountains. The southern coast lies 300 km from any plate edge. Card B, earthquake map: each dot is a past earthquake. Dots crowd along the coastal stretch of the plate edge and along the mountain stretch; the southern coast has only 3 dots. Card C, building rule: Ardmoor's code asks every building to withstand the largest earthquake with a 10% chance of happening at its own site within 50 years. Ways to build for it include strong, flexible frames and base isolation, which lets a building move apart from the ground's shaking. Card D, two sites from the hazard map: Site 1, the harbor, 12 km from the plate edge, has 60 dots within 50 km, and its 10%-in-50-years earthquake would shake it strongly. Site 2, a plains town on the southern coast, has 3 dots within 50 km, and the same likelihood gives weak shaking there.

2. 1.

   Which reading of Cards A and B fits the dots along the coast and the Veld Mountains, Luz asks?

   • The dots follow the plate edge, even where it turns inland, so the edge explains them better than the coast
   • The dots follow the coastline, since they crowd along the coast where the plate edge runs
   • The dots follow mountains, since the Veld Mountains have many dots and mountains themselves cause earthquakes
   • The dots spread evenly along the whole coast, so the plate edge makes no difference
3. 2.

   Milo sees that the southern coast, 300 km from any plate edge, has 3 dots. What do Cards A and B support?

   • That coast is safe from earthquakes, since earthquakes need a plate edge to start
   • Earthquakes can occur away from plate edges, but far less often than along them
   • The three dots show that a hidden plate edge must run along that coast too
   • The three dots are map errors, since dots belong near plate edges
4. 3.

   Noah asks whether Ardmoor's code (Card C) requires the same building strength at Site 1 and Site 2 (Card D).

   • No: the code is tied to each site's own earthquake, which shakes Site 1 strongly and Site 2 weakly
   • No: Site 2 has no plate edge nearby, so the code does not apply there
   • Yes: a Site 1 earthquake could someday reach Site 2, so Site 2 must resist strong shaking
   • Yes: the code names one likelihood, 10% in 50 years, so each building must be equally strong at either site
5. 4.

   A hospital at Site 1 uses base isolation. Pia asks what that choice and Card C say.

   • It is required by the code at strong-shaking sites, so each such building must use it
   • It stops the ground at Site 1 from shaking under the building
   • It replaces the code, since a building that moves apart from the ground needs no strength rule
   • It is one way to meet the strong-shaking requirement; the code sets the target, not the method
6. 5.

   A planner says Site 1's 60 dots against Site 2's 3 mean 20 times the strength. What does Card C support, Ren asks?

   • The planner is right: 60 against 3 is 20 times, so the code scales building strength with the dot counts
   • Strength follows the shaking of each site's own earthquake; a ratio of dot counts is not a ratio of strength
   • Strength should scale with distance from the plate edge: 12 km against 300 km
   • Neither site needs a rule, since dots record the past and cannot guide the design of new buildings
7. 6.

   Tala's note: 'Earthquakes happen only on plate edges, so a town 300 km from an edge needs no earthquake-resistant building.' Which fix fits the cards?

   • Towns far from edges need the same strength as the harbor, because the code ignores distance
   • Change nothing; 3 dots on the southern coast are too few to count
   • Soften the first word to 'mostly'; the rest stands, because 300 km from an edge is too far for any shaking
   • Earthquakes cluster near edges but occur elsewhere, and Site 2 still needs strength for its weak shaking

8. Use this

   Card E, Tamsin (an invented island, made up for practice). Map 1, landforms and plates: a plate edge runs along the whole west coast; no other plate edge lies on the island. Hills fill the north and a low plain lies in the south. Map 2, hazards: earthquake dots crowd along the west coast, and none lie in the hills. Storm-track arrows from the warm eastern sea reach the east coast and the south plain in most years; none cross the northern hills. Card F, people on Tamsin (invented numbers): west coast 90,000; east coast 50,000; south plain 40,000; northern hills 20,000.

9. 7.

   Which reading of both Tamsin maps fits the east coast, Zee asks?

   • Storms and quakes both come from plate edges, so the arrows show a hidden edge offshore
   • The maps show storm arrows but no plate edge or dots there, so storms, not quakes, are the hazard to plan for
   • The dots stop at the east coast because quakes cannot happen there, so storms will remain the hazard
   • Map 1 shows no plate edge on the east coast, so it faces no hazard on these maps
10. 8.

    Esme's note: 'The arrows prove a storm will hit the south plain next year.' Which fix fits Cards E and F?

    • Say the arrows show past storms reached the south plain in most years, so its 40,000 people should plan for storms
    • Change the first verb to 'show' but keep 'next year', since arrows that reach the plain in most years show a storm is coming
    • Delete the note: arrows from past storms are no evidence about the plain
    • Say the arrows show 40,000 people will be hit next year, since that is the plain's population
11. 9.

    Tamsin's agency will run one school drill type in each area. Which plan fits both maps best, Jun asks?

    • Earthquake drills in west-coast schools and storm drills in east-coast and south-plain schools
    • Earthquake drills in the hills, since hills are land raised by the same plates as the dots
    • Storm drills on the west coast, since schools beside any coast face the sea
    • Both drills in each area, since dots and arrows could move next year
12. 10.

    Which statement about Tamsin's west coast is best supported by Cards E and F, Kira asks?

    • The south plain faces no earthquake risk, since the dots crowd along the west coast
    • Its many dots mean many past earthquakes, so a building there faces a quake more often than in the hills
    • Its dots mean quakes there are stronger than anywhere else on Tamsin
    • Its dots mean an earthquake is overdue there, since the dots have not yet been followed by a big one on the coast