Quake and Tsunami Strike New Zealand

WORLD

Teachers, scroll down for a quick list of key resources in our Teachers’ Toolkit, including today’s simple MapMaker Interactive map.

Discussion Ideas

In our video “Earthquakes 101,” we learn that most earthquakes are caused by the movement of tectonic plates far below Earth’s surface. What tectonic plates were interacting in the earthquake that struck New Zealand? Take a look at today’s simple MapMaker Interactive map for some help.
- The Pacific plate and the Australian plate (sometimes called the Indo-Australian plate) were interacting.

How were the plates interacting? Take a look at the classic Nat Geo map of “Earth’s Dynamic Crust” for examples of different types of tectonic activity.
- “The plate boundary in the region of the earthquake is complex, involving a transition from subduction along the Hikurangi Trough to the east of the North Island, to transform faulting through the South Island.” So, the plates are interacting in two major ways.
  - Subduction! (It’s our favorite geologic process.) According to the “Earth’s Dynamic Crust” map, “Colliding with the edge of a continent [Australia], old, cold, heavy seafloor [the Pacific] drives back into the interior of the Earth and forms an ocean trench [the Hikurangi Trough].”
  - Transform faulting! According to the “Earth’s Dynamic Crust” map, “Grinding past each other in fits and starts, plates leave great rips, or faults, in their journey. Strain builds up along ‘locked’ plate edges; the stress can be released gradually by thousands of tiny earthquakes or released in a single disastrous jolt.” Seismologists think the quake may have been such a jolt—a “triggered slip on the Pacific:Australia subduction zone interface.”

The New Zealand quake is described of having a magnitude of about 7.8. What is magnitude? Is 7.8 a high magnitude?
- Magnitude is a number that describes the intensity or size of an earthquake. Our “Earthquakes 101” video talks about the Richter scale of magnitude, but seismologists are far more likely to use the moment magnitude scale (MMS or simply M).
- A 7.8 quake has a very high magnitude. The Great San Francisco Earthquake of 1906 had about a 7.8 magnitude, as did the devastating Nepal quake that struck last year.

The New Zealand quake is described as having a focal depth of about 23 kilometers (14.3 miles). What is focal depth? Is 23 kilometers a deep or shallow focal depth?
- The focal depth of an earthquake is how far below the surface of an earthquake’s epicenter the actual rupture, slip, or dip took place.
- Earthquakes can take place anywhere between one and 700 kilometers below Earth’s surface, so 23 kilometers is a pretty shallow depth.

What does the earthquake have to do with the tsunami that is leading to evacuations? Watch our video on tsunamis for some help.
- The tsunami was triggered by the movement of the seafloor caused by the earthquake. “Potentially imperceptible in deep water,” according to the video, “a tsunami increases in height as it encounters the shallow waters of shore.”

TEACHERS’ TOOLKIT