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How big is a small earthquake? Challenges in determining microseismic magnitudes

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)51-56
Number of pages6
JournalFirst Break
Issue number2
Early online date1 Feb 2019
DateAccepted/In press - 5 Jan 2019
DateE-pub ahead of print - 1 Feb 2019
DatePublished (current) - 1 Feb 2019


Earthquake magnitudes are surprisingly difficult to estimate accurately. This is especially true when evaluating small earthquakes: for example, those caused by human activities such as shale gas stimulation, CO2 and waste water storage, and enhanced geothermal systems. Uncertainties are created by a range of issues including: which ‘magnitude’ scale is used; what type of instrument records the earthquake; how the instruments are deployed; and the heterogeneity of the Earth between the source and the receivers. Errors can be larger than an order of magnitude in scale. For very small earthquakes this is not usually of much concern. However, occasionally, larger earthquakes induced by human activity are felt at the surface. This has led to regulatory frameworks that require accurate assessment of earthquake magnitudes before they reach the point of being felt. Hence, to monitor and mitigate felt seismicity there is a need to calculate accurate earthquake magnitudes in real time. Regulatory monitoring of induced seismicity is becoming a key issue in the successful development of reservoir projects that involve stimulation or storage. Here, we discuss the challenges with implementing such reservoir monitoring, and provide a suggested monitoring strategy.



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