#Known seismicity Microseismicity has been observed at Rotokawa since the start of deep injection in 2005 \cite{Sherburn&B&B_2011} \cite{Sherburn&B&B_2012} \cite{Sherburn_2015} and at Ngatamariki since injection operations began in 2012 \cite{Sherburn&Bourguignon_2013}. Some of this activity is accounted for by background, natural seismicity associated with the geothermal fields' location within the tectonically active TVZ. However, a much larger part of the microseismicity at Ngatamariki and Rotokawa is due to changes in the reservoir associated with deep fluid injection. Critically stressed and favourably oriented fractures within and adjacent to the geothermal resource can be activated by both pressure changes induced by power plant operations and thermal contraction of the hot reservoir rocks as the cooler condensate and brine is injected \cite{Sherburn_2015}. At Rotokawa and Ngatamariki, pressure drawdown across most of the reservoir suggests that thermal contraction may be the dominant source of microseismicity in areas not immediately adjacent to injection wells, which are subject to localized pressure increases on the scale necessary to generate microearthquakes \cite{Sherburn_2015}.
At Rotokawa, the largest portion of microseismiciy since 2012 has been located in the southeast portion of the field as discussed in \cite{Sherburn_2015}, within the polygon shown in Figure \ref{Figure2} at a depth of 1-3 km below sea level \cite{Sherburn_2015}. Much of this seismicity is likely related to the Central Field Fault which divides the injection and production areas at Rotokawa and acts as a barrier to cross-strike movement of reservoir fluids \cite{Sherburn_2015}. Since operations began at Ngatamariki, the total number of detected events at Rotokawa has outnumbered that of Ngatamariki by a factor of roughly three \cite{Sherburn&B&B_2013} \cite{Sherburn&J&B_2014} \cite{Sherburn&Johnson_2015}.
At Ngatamariki, two very distinct clusters of microseismicity are observed, one in the North of the field and one further south (see Figure \ref{Figure2} \cite{Sherburn&Bourguignon_2013} \cite{Sherburn&Bourguignon_2014} \cite{Sherburn&Bourguignon_2015}. The northern cluster has been observed in the northern injection area surrounding wells NM08 and NM09 (Figure \ref{Figure1}) at a depth of between 1.5 and 2.5 km below sea level whereas the southern cluster is generally located between the injection area at NM10 and NM06 and the production area for the field surrounding NM05 (Figure \ref{Figure1})\cite{Sherburn&Bourguignon_2015}. This southern cluster is likely associated with a structure related to the Aratiatia Fault Zone which strikes SW-NE across the southern end of the Ngatamariki field (Figure \ref{Figure1}) as has been modeled by \cite{buscarlet2015reservoir}. Events have been observed in roughly equal numbers in both clusters \cite{Sherburn&Bourguignon_2013} but the total number of events detected at Ngatamariki has consistently been about one third of the number detected at Rotokawa \cite{Sherburn&Bourguignon_2013} \cite{Sherburn&Bourguignon_2014} \cite{Sherburn&Bourguignon_2015}.