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Early Parameters of Seismograms: What Influences Them and Are They Useful in Understanding Earthquake Determinism?

Description: 

It is reasonably simple to determine the magnitude of an earthquake after it has happened. However, it is unclear to what extent an earthquake’s final magnitude is ‘known’ before rupture ends. We are interested in whether features of the initial stages of an earthquake can make accurate predictions about the earthquake's final size: whether earthquakes are deterministic. This is not a new question, and several approaches have been taken in the past. For example, Olson and Allen (2005) found a relationship between the final magnitude and predominant period of the first 4 seconds of earthquakes. However, the results remain controversial, partly because they and subsequent researchers analyzed only moderate numbers of earthquakes, and examined long windows of time relative to the durations of most earthquakes. The increase in data availability and quality over the last 15+ years now allows us to re-investigate this issue in a more statistically robust way.

We examine the beginning of ~8000 earthquakes from around the world. We quantify the predominant period, average period, integral of velocity squared (IV2) and peak ground displacement (PGD) in time windows ranging from 0.3 to 4 s, and investigate their relationships with magnitude. We find the strongest relationships with PGD and IV2. Whilst these relationships are strongest in the longest windows, they do persist as we look at increasingly shorter windows. For other parameters such as predominant period, we see a relatively constant correlation coefficient as we increase the calculation window duration, but see a decreasing correlation as we increase the minimum magnitude of the dataset, regardless of calculation window length. We then propose physical mechanisms for these observations.

Session: Earthquake Source Parameters: Theory, Observations and Interpretations

Type: Oral

Date: 4/18/2023

Presentation Time: 09:00 AM (local time)

Presenting Author: Rebecca Colquhoun

Student Presenter: Yes

Invited Presentation: 

Authors