Magnitude reassessment of New Zealand earthquakes

Abstract

SUMMARYThe surface-wave magnitudes of a selection of New Zealand earthquakes have been determined on a consistent basis using the 'Prague formula' and station corrections. The earthquakes range in magnitude from about 5 to 7.8, covering the instrumental period . Magnitudes for many of the earlier events had not been properly determined previously; and some significant discrepancies from the traditional magnitudes were found.The use of European station data (160" < D < 175") is important to New Zealand because of its geographical isolation. These distant data were found to ghe consistently slightly higher M, than closer stations, but could be used without bias through the station correction procedure. The relationship between M , and ML was found for 31 'shallow' New Zealand events and much of the scatter was explained as a function of depth. Significant differences in M J M , expressions from Europe and California were also found.The limited New Zealand data for M , and M , related well to Californian and global relationships with M,.

The 1968 May 23 Inangahua, New Zealand, earthquake: An integrated geological, geodetic, and seismological source model

“…comm. ); M s 1 A (Dowrick & Smith 1990;Dowrick 1991); and (moment magnitude) M w 7.1 (Anderson et al 1993). The discrepancy between M w and M s values is unusual in that most other large South Island earthquakes that have been compared show closer agreement but with the M s value lower (Anderson et al 1993).…”

Focal mechanisms of large earthquakes in the South Island of New Zealand: implications for the accommodation of Pacific-Australia plate motion

“…Focal mechanisms for New Zealand earthquakes are often difficult to determine reliably from P-wave first-motion data alone. Events smaller than magnitude 6 are generally too small for their first motions to be unambiguously recorded 5.8* 5.9 5.8 6.1 5.6* 5.8 7.4* 7.1 6.2' 6.3 5.5* 5.7 6.4* 6.5 7.2* 7.3 6.1* 6.1 6.0 6.2 6.7* 6.7 6.2 6.4 5.3t 5.8 5.6t 6.0 6.0t 5.9 * M,$ value from Dowrick & Smith (1990) or Dowrick (1991). t M,$ value from Preliminary Determination of Epicentres, Monthly bulletin, National Earthquake Information Service.…”

New predictive equations for Arias intensity from crustal earthquakes in New Zealand

“…For the majority of events in the dataset, focal mechanism solutions exist, and for some, The shaded columns indicate the datasets used to derive the final predictive equations The columns L, W, h t , and h b correspond to the fault rupture length, rupture width, and depths to the top and bottom of the rupture surface respectively. Numbers in the Refs column correspond to the following references: (1) Anderson et al (1993), (2) Webb and Anderson (1998), (3) Dowrick and Rhoades (1998), (4) additional constraint is available in the form of spatial aftershock patterns, geodetic modelling, elastic dislocation modelling, Coulomb stress change modelling and considerations of structural geology. Information from the many references cited in Table 3 was extracted in order to determine the finite fault rupture parameters for each event.…”