**3. Waveform data analysis**

**Figure 1** shows the stations we used to locate the Miramichi aftershocks. The closest one to the sequence (about 25 km) was KLN. At this station clear Pg- and Sg-phase were recorded for almost all aftershocks. **Figure 3** shows 10 seismograms generated by 10 aftershocks, recorded at KLN. The top 5 traces were generated by the aftershocks

#### **Figure 3.**

*Vertical component short period displacement seismograms recorded at KLN (along a displacement trace, sPg phase is easier to identify than along a velocity trace), generated by 10 aftershocks in* **Table 1***. All records are aligned at the Pg phase. The time on the left side of each record is the raw record start time. For each aftershock, the hypocentral distance to KLN is mainly constrained by the time difference TSg – TPg, while the focal depth is mainly constrained by TsPg– TPg. The top 5 records were generated by the aftershocks in the right group, while the bottom 5 records by aftershocks in the left group (see* **Figure 2***). The 10 aftershocks were selected along a line which is orthogonal to the located epicenter distribution trend (about Az 38°, see* **Figure 2***). The TSg – TPg times along the top 5 records are shorter than those along the bottom 5 records; due to those epicenters to KLN are shorter. The time difference δt corresponds to the spatial gap between the two groups.*

in the right group (see **Figure 2**), while the bottom 5 traces by aftershocks in the left group. The *T*Sg *– T*Pg times along the top 5 traces are shorter than those along the bottom 5 traces; due to those epicenters to KLN are shorter (refer to **Figures 1** and **2**).

The second closest station was EBN (about 135 km from the sequence). At EBN, the onset of the Pg phase was usually clear on the seismograms generated by aftershocks with *m*<sup>N</sup> ≥ 2.8, so the arrival time of the Pg phase could be measured. **Figure 4** shows vertical displacement seismograms recorded at EBN. The trace indicated with mb 5.4 was generated by the mb 5.4 aftershock. The trace indicated with mb 5.0 was generated by the mb 5.0 aftershock. The other 4 traces in the top panel were generated by 4 aftershocks in the left group; the 5 traces in the bottom panel were generated by 5 aftershocks in the right group (see **Figure 2**). The *T*Sg *– T*Pg times (about 16.54 s) along the traces 2, 3, 4, and 5 in the top panel, are shorter than those (about 17.04 s) along the bottom 5 traces; due to those aftershocks in the left group are closer to EBN. The *T*Sg *– T*Pg times along the traces generated by the two principal aftershocks in the bottom panel are approximately equal; implying that they are in the same group.

The third closest station was GGN (station distance ~200 km). At this station, the Pn phase generated by aftershocks with *m*<sup>N</sup> ≥ 2.8, was clear (see **Figure 5**).

The waveforms at station LMN (station distance ~200 km; **Figure 1**) were also analyzed. The Pn phase, generated by aftershocks with *m*<sup>N</sup> ≥ 2.8, was clear when the

#### **Figure 4.**

*Vertical component short period displacement seismograms recorded at EBN (station distance ~ 135 km) generated by 9 aftershocks in the Miramichi sequence. The trace indicated with mb 5.4 was generated by the mb 5.4 aftershock. The trace indicated with mb 5.0 by the mb 5.0 aftershock. The other 4 traces in the top panel were generated by 4 aftershocks in the left group; the other 3 traces in the bottom panel were generated by 3 aftershocks in the right group (see Figure 2). For each aftershock, the hypocentral distance to EBN is mainly constrained by the time difference TSg – TPg. The TSg – TPg times (about 16.54 s) along the traces 2, 3, 4, and 5 in the top panel are shorter than those (about 17.04 s) along the bottom 5 traces; due to those epicenters to EBN are shorter.*

*Locations of the 1982 Miramichi (Canada) Aftershocks: Implication of Two Rupture Regions… DOI: http://dx.doi.org/10.5772/intechopen.108195*

#### **Figure 5.**

*Travel time comparisons. The upper three traces were generated by the master event (ME, No. 36 in* **Table** *1); the bottom three traces were generated by a secondary event (SE, No. 44 in* **Table** *1). The time marked along the bottom axis is relative for conveniently aligning the traces. The symbol t0 means origin time;* ∆*Pg,* ∆*Sg, and*  ∆*Pn are travel time differences. The origin times of the ME and SE were aligned for comparison (the determined values of the two origin times are in* **Table** *1; here they were calculated using Sg - Pg times). The travel times for the ME at KLN: Pg phase is 4.00 s and Sg phase is 6.97 s; at EBN: Pg is 22.15 s; at GGN: Pn is 31.07 s. the travel times for the SE at KLN: Pg phase is 3.58 s and Sg phase is 6.22 s; at EBN: Pg is 22.65 s; at GGN: Pn is 30.71 s. At KLN:* ∆*Pg is + 0.42 s (4.00–3.58) and* ∆*Sg is + 0.75 s (6.97–6.22); at EBN:* ∆*Pg is − 0.50 s (22.15–22.65); at GGN:*  ∆*Pn is + 0.36 s (31.07–30.71). These differences determine the relative positions of the two aftershocks. These traces are vertically enlarged, horizontally expanded, and interpolated to 100 points/s, the arrival times could be measured with a precision of 0.01 s.*

seismograph at this station operated normally. Unfortunately, in 1982, the seismograms at LMN were often rectangular pulses with different amplitudes (probably due to instrument malfunction), so the Pn arrival times could only be measured for some aftershocks. As such, the waveform records were not used for the locations.

The Pn phase at stations LPQ and GSQ are also clear for aftershocks with magnitude *m*<sup>N</sup> ≥ 3.5. The Pn phase at these two stations and at GGN, as well as Pg and Sg at EBN were used to locate the mb 5.4 aftershock.
