Earthquake FAQ

Frequently asked questions about earthquakes.

• Q: What causes earthquakes in New Zealand?
• A: The Earth's entire outer surface is like a hard shell, which is made up of smaller pieces called 'plates'. Under New Zealand, two of these plates are colliding with huge force causing one to slowly grind under the other; this ongoing process causes our earthquakes.
  
  
• Q: What is an earthquake swarm?
• A: A sequence of earthquakes that strike in a short period of time, located in close vicinity to each other.
  
  
• Q: Does a swarm mean the 'big one' is coming?
• A: No. Although large earthquakes are sometimes preceded by smaller associated earthquake swarms (called foreshocks), swarms of seismic activity do not necessarily indicate that a large earthquake is to follow.
  
  
• Q: How many earthquakes happen in New Zealand each year?
• A: GeoNet records around 15,000 earthquakes in and around New Zealand each year; most of these are small but up to around 250 are big enough to be felt.
  
  
• Q: I felt an earthquake - why isn't it on the GeoNet website?
• A: Earthquakes are posted on the website if they were felt by several people or are of significant magnitude. These are usually posted within 30 minutes once the duty officer has located the earthquake. If you felt an earthquake we suggest you complete a GeoNet Felt Earthquake Report.
  
  
• Q: Why is there activity on the drums when no earthquake is occurring?
• A: The seismometers that we use are very sensitive instruments and can sometimes be triggered by unrelated phenomena like weather or traffic. This signal is recorded as 'noise' on the seismograph.
  
  
• Q: What do the characters on the top left of a seismic drum? For example, what about MRZ/10-SHZ/NZ?
• A: This uniquely identifies the seismic trace you are viewing:
  • The first part MRZ shows the international seismic station code, in this case "Mangatainoka River".
  • The second part 10 shows the location code of the seismometer at Mangatainoka River.
  • The third part SHZ is defined by the SEED convention, and indicates the characteristics of the seismometer in use.
  • The fourth part NZ shows the network code, in this case "New Zealand".
    
    
• Q: Where can I find information on New Zealand earthquakes that occurred over a period of time, or in a certain region?
• A: The Quake Search function on the GeoNet website allows the user to extract a file of earthquake locations in New Zealand. The search can by done using date, geographic location, focal depth or magnitude.
  
  
• Q: What was the biggest earthquake in New Zealand's history? How about the world?
• A: The biggest known earthquake in New Zealand was the 1855 magnitude 8.2 in the Wairarapa; around 5000 km² of land was shifted vertically during the earthquake. The largest earthquake recorded in the world in the last 100 years was the 1960 magnitude 9.5 earthquake in Chile. It caused 5700 deaths and created a large tsunami.