**3.1. Number of lineaments and line length analysis**

The resultant lineament maps produced for all temporal images of the two study areas. Thereafter, line length information was calculated (converted in kilometer) and phase wise lineament behavior changes were observed in the presence (prior to strike) and the absence of earthquake event. The spatial distribution of lineaments of Gorkha-Nepal from 31 January 2015 to 7 May 2015 and of Imphal-Manipur from 19 March 2015 to 17 January 2016 are generated and used in overlay analysis purpose, representing with two distinct black lines (light and solid) with line weights values 0.50 and 1.25, respectively are used for each anomaly phase detection. In each phase of anomaly, every initial image was highlight with light black line and afterwards image is displayed with solid black line. In the same way, different phases were represented as normal (absence of Earthquake), initial (presence of Earthquake), middle (presence of Earthquake), strong phase (presence of Earthquake), and post-earthquake phase, respectively. In addition, corresponding statistical information of lineaments for both study areas was generated and presented in **Table 2** for case 1 and **Table 3** for case 2.

The extracted data prior to the earthquake suggest that a major number of lineaments and total number of lineaments vary from 31,613 on 20 March 2015 to 34,641 on 21 April 2015 (earthquake strike on 25 April 2015). The total lineament was certainly dropped to 27,025 in number in just 4 days before the main event. This anomaly was quite high in respect with the


Brackets terminology in the 1st column refers that lineament anomaly-no means normal behavior of lineaments, and anomaly-yes means abnormal behavior of lineaments; in the 2nd column, b refers before earthquake and a refers after earthquake (earthquake occurrence date: 25 April 2015). Source: data extracted using PCI Geomatica-9.1, ArcGIS 10.5.

**Table 2.** Statistical information of the extracted lineament of Gorkha of Nepal and its adjoining areas.


(PCA). Epicenter-based single tile images were considered to observe the changes of the lin-

The following sections (3.1–3.4) represent the present research derived results, based on three different situations. First, results highlight automatic extraction of lineaments data along with lineament length information; second, temporal data-based lineament fluctuations observed by applying vector overlay technique of ArcGIS 10.5 software, and third, rose diagram was created to know the directional changes. Finally, the overall integrated assessment and statistical information-based lineament change comparison were performed for the two impending earthquakes. The present significant contribution of the lineament data suggests that data have potential enough to detect pre-earthquake anomaly in advance without having integra-

The resultant lineament maps produced for all temporal images of the two study areas. Thereafter, line length information was calculated (converted in kilometer) and phase wise lineament behavior changes were observed in the presence (prior to strike) and the absence of earthquake event. The spatial distribution of lineaments of Gorkha-Nepal from 31 January 2015 to 7 May 2015 and of Imphal-Manipur from 19 March 2015 to 17 January 2016 are generated and used in overlay analysis purpose, representing with two distinct black lines (light and solid) with line weights values 0.50 and 1.25, respectively are used for each anomaly phase detection. In each phase of anomaly, every initial image was highlight with light black line and afterwards image is displayed with solid black line. In the same way, different phases were represented as normal (absence of Earthquake), initial (presence of Earthquake), middle (presence of Earthquake), strong phase (presence of Earthquake), and post-earthquake phase, respectively. In addition, corresponding statistical information of lineaments for both study

The extracted data prior to the earthquake suggest that a major number of lineaments and total number of lineaments vary from 31,613 on 20 March 2015 to 34,641 on 21 April 2015 (earthquake strike on 25 April 2015). The total lineament was certainly dropped to 27,025 in number in just 4 days before the main event. This anomaly was quite high in respect with the

> **Length (km)-min**

Brackets terminology in the 1st column refers that lineament anomaly-no means normal behavior of lineaments, and anomaly-yes means abnormal behavior of lineaments; in the 2nd column, b refers before earthquake and a refers after earthquake (earthquake occurrence date: 25 April 2015). Source: data extracted using PCI Geomatica-9.1, ArcGIS 10.5.

**Table 2.** Statistical information of the extracted lineament of Gorkha of Nepal and its adjoining areas.

31 Jan 2015 (anomaly-no) 85 (b) 11,080 0.001 11.476 1.627 18025.26 0.808 20 Mar 2015 (anomaly-yes) 36 (b) 31,613 0.030 31.658 0.677 21409.09 0.613 5 Apr 2015 (anomaly-yes) 20 (b) 27,025 0.030 31.666 0.670 18116.14 0.680 21 Apr 2015 (anomaly-yes) 4 (b) 34,641 0.060 17.426 0.634 21973.44 0.397 7 May 2015 (anomaly-yes) 12 (a) 25,917 0.030 31.666 0.632 16382.09 0.681

**Length (km)-max** **Mean value (km)** **Sum value (km)**

**SD value (***σ***)**

tion of processed satellite imageries, geological map and field validation data.

areas was generated and presented in **Table 2** for case 1 and **Table 3** for case 2.

eaments related to both the earthquakes.

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**3.1. Number of lineaments and line length analysis**

**Date of image acquisition Days** 

**(b/a)**

**No. of lineament** Brackets terminology in the 1st column refers lineament anomaly-no, means normal behavior of lineaments and anomaly-yes, means abnormal behavior of lineaments and in the 2nd column b refers before and a refers after earthquake (earthquake occurrence date: 4 January 2016). Source: data extracted using PCI Geomatica-9.1, ArcGIS 10.5.

**Table 3.** Statistical information of the extracted lineament of Imphal, Manipur and its surrounds, Eastern India.

absence of earthquake, where only 11,080 lineaments observed (85 days before) (**Table 2**), whereas the number of lineaments was found decreasing (25,917) in post-earthquake phase (12 days after the earthquake) probably due to the release of strain and structural damage done by the high magnitude earthquake (7.8 Mw), compared to its three-preceding anomaly phases. The real cause is unclear till now regarding why the change was occurred prior to earthquake strike. However, simple explanations have been given only based on the experimental output from the extracted lineament results.

The lineament changes and anomalous behavior also observed through line length statistics (**Table 2**). Total line length was observed 18025.26 km, the minimum and maximum values were found quite low and the SD value was observed the highest in the absence of earthquake event. The anomaly phases were observed in the presence of earthquake event, where the maximum length and the SD value were found almost similar in 36, 20 days before earthquake (20 March and 5 April 2015), but not similar in 4 days before earthquake (21 April 2015). The mean length was dropped 0.043 km along with the maximum and SD length of lineament (in km) was sharply decreased (**Table 2**), representing high abnormal behavior (strong anomaly) prior to earthquake event. The same variables of lineament were found increased after the earthquake event (12 days later), as high magnitude of earthquake already ruptured in this region. There was a tendency of lineament to return to its original status but failed completely to return to its initial situation.

On the other hand, similar method applied over Imphal, Manipur (6.7 Mw) earthquake assessment. The total number of lineaments observed 14,524 in number (**Table 3**), representing "no anomaly" in the absence of earthquake event (292 days before). However, the lineament distribution during 30 November 2015 to 17 January 2016 represents the abnormal behavior. The number of lineaments was sharply decreased (4660) from initial to middle phase (30 November 2015 to 16 December 2015). The total number of lineaments found the highest in number (62,332) than its all four preceding values, observed in the post-earthquake stage (**Table 3**).

#### **3.2. Lineament fluctuations observation through overlay analysis**

As mentioned in Section 2.3.2 under Section 2.3 (on methodology), lineament fluctuations changes were observed based on temporal data. **Figures 5(a**–**g)** and **6(a**–**g)** represent temporal lineament fluctuations over Gorkha of Nepal and Imphal of Manipur regions, respectively.

**Figure 5a** represents the fluctuations of the lineaments on 20 March 2015 (36 days before: light black color) to 5 April 2015 (20 days before: solid black color) in the presence of earthquake event. Thereafter, the abovementioned data overlay with 21 April 2015, where significant fluctuations of lineaments were observed around epicenter regions 4 days before earthquake strike (see southern part of image, **Figure 5b**). These data were further overlay with post-

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However, **Figure 5d** illustrates the lineament fluctuations in the presence (4 days before) and the absence of earthquake event (85 days before) and highlights with pink color to ensure that anomaly exists over this region. Sudden increase of lineaments around epicenter region represents the abnormality over this region. This means that anomalous and unexpected fluctuations observed in lineament data on this particular date. **Figure 5e** also represents the lineament fluctuations in the presence (20 days before) and the absence of earthquake (85 days before). The fluctuations were also slightly noticed in the initial phase (36 days before) compared with the absence of earthquake event (**Figure 5f**). In the final stage, it compares fluctuations both in the absence of earthquake, though observed lineaments try to readjust but not

On the other hand, similar technique was applied to know the lineament fluctuations for the Imphal-Manipur earthquake, and according to USGS, it was categorized as strong earthquake (6.7 Mw). **Figure 6** represents the lineament fluctuations over these areas in the absence and the presence of earthquake event, later compares with post-earthquake data. **Figure 6a** represents lineament fluctuations observed from 36 days (30 November 2015) and 20 days (16 December 2015) before earthquake, clearly noticed from epicenter and adjoining areas. However, it is mentioned here that, at this stage, few lineaments didn't observe due to presence of clouds on image. In the same way, fluctuations were observed comparing with 20 days and 4 days before lineaments data (**Figure 6b**). Five different colors were used for fluctuation comparison in the Imphal-Manipur regions similar to Gorha-Nepal regions. The unusual lineament behaviors were observed when compared 4 days before earthquake with 13 days after earthquake (**Figure 6c**). Thereafter, anomaly observed when it has been compared 36 days before (solid black color) (in the presence of earthquake event) with 292 days before data (light black color) (in the absence of earthquake event) (**Figure 6d**). The number of lineaments observed high in number, representing anomalous behavior around epicenter and its near adjoining areas. However, the sudden lineament fluctuations were also observed 20 days before compared to 292 days before in the absence

The highest number of variations of lineaments observed prior to 4 days before earthquake (solid black color) compared to 292 days before earthquake (light black color) in the absence of earthquake event and detected the highest anomalies for the Imphal-Manipur earthquake epicenter and adjoining regions in the presence of earthquake event (**Figure 6f**). Whereas, the lineament data anomaly still present and found extreme number of lineaments probably due to massive geological activities done by this earthquake. This unexpected behavior was noticed only after the earthquake event (**Figure 6g**) compare to normal time lineament data (292 days before: showing in light black color), indicate another probable strong earthquake will immediately occur.

earthquake lineament data, which try to return to its earlier position (**Figure 5c**).

matched exactly with the normal condition (see **Figure 5g**).

of that event (**Figure 6e**).

**Figure 5.** Lineaments fluctuations observed through overlay analysis of Gorkha of Nepal regions: (a) lineament fluctuations observed in the presence of earthquake event (comparing 36 and 20 days before earthquake), (b) same as observed in 36 days and 4 days before earthquake, (c) 4 days before and 12 days after), (d) highly observed fluctuations representing strong phase (4 days and 85 days before), (e) 20 days and 85 days before earthquake (in the presence and the absence of earthquake), (f) same fluctuations comparison between 20 March 2015 and 31 Jan 2015 (the presence and the absence of earthquake event) and (g) lineaments fluctuations in between 7 May 2015 (post-earthquake) and 31 January 2015 (in the absence of earthquake event). The earthquake epicenter was marked with the black dotted circle point symbol.

**Figure 5a** represents the fluctuations of the lineaments on 20 March 2015 (36 days before: light black color) to 5 April 2015 (20 days before: solid black color) in the presence of earthquake event. Thereafter, the abovementioned data overlay with 21 April 2015, where significant fluctuations of lineaments were observed around epicenter regions 4 days before earthquake strike (see southern part of image, **Figure 5b**). These data were further overlay with postearthquake lineament data, which try to return to its earlier position (**Figure 5c**).

However, **Figure 5d** illustrates the lineament fluctuations in the presence (4 days before) and the absence of earthquake event (85 days before) and highlights with pink color to ensure that anomaly exists over this region. Sudden increase of lineaments around epicenter region represents the abnormality over this region. This means that anomalous and unexpected fluctuations observed in lineament data on this particular date. **Figure 5e** also represents the lineament fluctuations in the presence (20 days before) and the absence of earthquake (85 days before). The fluctuations were also slightly noticed in the initial phase (36 days before) compared with the absence of earthquake event (**Figure 5f**). In the final stage, it compares fluctuations both in the absence of earthquake, though observed lineaments try to readjust but not matched exactly with the normal condition (see **Figure 5g**).

On the other hand, similar technique was applied to know the lineament fluctuations for the Imphal-Manipur earthquake, and according to USGS, it was categorized as strong earthquake (6.7 Mw). **Figure 6** represents the lineament fluctuations over these areas in the absence and the presence of earthquake event, later compares with post-earthquake data. **Figure 6a** represents lineament fluctuations observed from 36 days (30 November 2015) and 20 days (16 December 2015) before earthquake, clearly noticed from epicenter and adjoining areas. However, it is mentioned here that, at this stage, few lineaments didn't observe due to presence of clouds on image. In the same way, fluctuations were observed comparing with 20 days and 4 days before lineaments data (**Figure 6b**). Five different colors were used for fluctuation comparison in the Imphal-Manipur regions similar to Gorha-Nepal regions. The unusual lineament behaviors were observed when compared 4 days before earthquake with 13 days after earthquake (**Figure 6c**). Thereafter, anomaly observed when it has been compared 36 days before (solid black color) (in the presence of earthquake event) with 292 days before data (light black color) (in the absence of earthquake event) (**Figure 6d**). The number of lineaments observed high in number, representing anomalous behavior around epicenter and its near adjoining areas. However, the sudden lineament fluctuations were also observed 20 days before compared to 292 days before in the absence of that event (**Figure 6e**).

The highest number of variations of lineaments observed prior to 4 days before earthquake (solid black color) compared to 292 days before earthquake (light black color) in the absence of earthquake event and detected the highest anomalies for the Imphal-Manipur earthquake epicenter and adjoining regions in the presence of earthquake event (**Figure 6f**). Whereas, the lineament data anomaly still present and found extreme number of lineaments probably due to massive geological activities done by this earthquake. This unexpected behavior was noticed only after the earthquake event (**Figure 6g**) compare to normal time lineament data (292 days before: showing in light black color), indicate another probable strong earthquake will immediately occur.

**Figure 5.** Lineaments fluctuations observed through overlay analysis of Gorkha of Nepal regions: (a) lineament fluctuations observed in the presence of earthquake event (comparing 36 and 20 days before earthquake), (b) same as observed in 36 days and 4 days before earthquake, (c) 4 days before and 12 days after), (d) highly observed fluctuations representing strong phase (4 days and 85 days before), (e) 20 days and 85 days before earthquake (in the presence and the absence of earthquake), (f) same fluctuations comparison between 20 March 2015 and 31 Jan 2015 (the presence and the absence of earthquake event) and (g) lineaments fluctuations in between 7 May 2015 (post-earthquake) and 31 January 2015 (in the absence of earthquake event). The earthquake epicenter was marked with the black dotted circle point symbol.

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**3.3. Lineament orientation change observation through rose diagram**

In this section, the lineament direction change has been observed in the absence and presence of earthquake event along with post-earthquake directional change, based on the method discussed on Section 2.3.3 under Section 2.3 (methodology). The case wise interpretation results based on lineament length data show normal and unusual behavior of lineament directions change ((**Figure 7(a**–**e)**—Gorkha and **Figure 8(a**–**e)**—Imphal). **Figure 7a** represents the direction of lineament during normal behavior (82 days before) with mean strike orientation of NE-SW direction (59.3 degrees-239.32 degrees), along with E-W and SE-NW directions also observed in the absence of earthquake. Whereas, the direction was start to move from 36 days before (20 March 2015) clearly represent that its mean strike line (101.8 degrees-281.85 degrees) was rotated enough (42.5 degrees) (**Figure 7b**) from normal condition (**Figure 7a**). **Figure 7c** represents directions were in ESE-WNW, E-W, NNE-SSW and N-S positions, where the mean strike direction (81.7 degrees-261.73 degrees) was rotated back and stay around 90° position (20 days before). Major direction was observed in ESE-WNW and NNE-SSW and another one N-E directional change firstly notice at this stage. Whereas, the direction was further rotated 23.7 degrees down

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**Figure 7.** Directional change measurement through rose diagrams for Gorkha, Nepal earthquake: (a) 31 January 2015, (b) 20 March 2015, (c) 05 April 2015, (d) 21 April 2015, and (e) 7 May 2015 (all diagrams based on temporal lineament data).

**Figure 6.** Similar overlay change analysis performed as **Figure 5** but for of Imphal of Manipur regions. Data representing changing behavior of lineament in the absence and presence of earthquake event. The panel represents (a) lineament fluctuations observed comparing 36 and 20 days before earthquake, (b) 20 days and 4 days before earthquake, (c) 4 days before and 13 days after, (d) highly observed fluctuations in the presence and the absence of earthquake (36 days and 292 days before), (e) 20 days and 292 days before earthquake (in the presence and the absence of earthquake), (f) fluctuations comparison between 4 days and 292 days before (presence and absence of earthquake event) and (g) lineaments fluctuations between 17 January 2016 (post-earthquake) and 19 March 2015 (in the absence of earthquake event).

#### **3.3. Lineament orientation change observation through rose diagram**

In this section, the lineament direction change has been observed in the absence and presence of earthquake event along with post-earthquake directional change, based on the method discussed on Section 2.3.3 under Section 2.3 (methodology). The case wise interpretation results based on lineament length data show normal and unusual behavior of lineament directions change ((**Figure 7(a**–**e)**—Gorkha and **Figure 8(a**–**e)**—Imphal). **Figure 7a** represents the direction of lineament during normal behavior (82 days before) with mean strike orientation of NE-SW direction (59.3 degrees-239.32 degrees), along with E-W and SE-NW directions also observed in the absence of earthquake. Whereas, the direction was start to move from 36 days before (20 March 2015) clearly represent that its mean strike line (101.8 degrees-281.85 degrees) was rotated enough (42.5 degrees) (**Figure 7b**) from normal condition (**Figure 7a**). **Figure 7c** represents directions were in ESE-WNW, E-W, NNE-SSW and N-S positions, where the mean strike direction (81.7 degrees-261.73 degrees) was rotated back and stay around 90° position (20 days before). Major direction was observed in ESE-WNW and NNE-SSW and another one N-E directional change firstly notice at this stage. Whereas, the direction was further rotated 23.7 degrees down

**Figure 7.** Directional change measurement through rose diagrams for Gorkha, Nepal earthquake: (a) 31 January 2015, (b) 20 March 2015, (c) 05 April 2015, (d) 21 April 2015, and (e) 7 May 2015 (all diagrams based on temporal lineament data).

**Figure 6.** Similar overlay change analysis performed as **Figure 5** but for of Imphal of Manipur regions. Data representing changing behavior of lineament in the absence and presence of earthquake event. The panel represents (a) lineament fluctuations observed comparing 36 and 20 days before earthquake, (b) 20 days and 4 days before earthquake, (c) 4 days before and 13 days after, (d) highly observed fluctuations in the presence and the absence of earthquake (36 days and 292 days before), (e) 20 days and 292 days before earthquake (in the presence and the absence of earthquake), (f) fluctuations comparison between 4 days and 292 days before (presence and absence of earthquake event) and (g) lineaments fluctuations between 17 January 2016 (post-earthquake) and 19 March 2015 (in the absence of earthquake

event).

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from middle phase representing 4 days before earthquake scenario, and two major trends ESE-WNW and N-S directions clearly be interpreted from this rose diagram (**Figure 7d**).

and the presence of earthquake data. **Figure 8a** illustrates the lineament directions of normal condition in the absence of earthquake event where major lineament positions were in NNE-SSW and minor lineament positions were in SE-NW and mean strike was in NE-SW directions with 46.8 degrees – 226.79 degrees angle. **Figure 8b**, 30 November 2015 (36 days before earthquake), suggests, ESE-WSW direction and mean strike (63.4 degrees – 243.43 degrees)

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**Figure 8c** represents 20 days before scenario (16 December 2015), it showed a major trend to be ESE-WNW (61.1 degrees – 241.11 degrees) with 2.3 degrees rotated back along with considering bin lengths another trend of NE-SW can also be exists. Besides those, on 1 January 2016 (prior to 4 days of earthquake events) two major trends NE-SW (61.7 degrees to 241.65 degrees) and ESE-WSW were identified by interpreting the lineament data (**Figure 8d**). Finally, **Figure 8e** represents the post-earthquake lineament direction (13 days after earthquake) which showed NE-SW (57.8 degrees – 237.83 degrees) from its immediate mean strike position data.

After fluctuations analysis of lineament data as shown in Section 3.2, few statistical test were performed in this section against number of lineament and length change. This statistical analyses were done based on the method discussed in Section 3.2.4 under Section 3.2, by using box-whisker for number of lineament and line trend by considering mean and SD value

The automatic extraction of lineament data values of both tables (**Tables 2** and **3**) suggests anomaly presence over the two study areas prior to earthquake strike, which was also observed even after the earthquake. On the other hand, the scenario was quite normal in the absence of earthquake event. The derived result illustrates different number of lineaments as observed through box plot and whiskers line chart (**Figure 9a**: Gorkha of Nepal; **Figure 10a**: Imphal of Manipur). However, line length value also differs in both cases (**Figure 9b**: Gorkha and **Figure 10b**: Imphal). These changes were noticed in our two cases, and probably due to

**Figure 9.** Results of number of lineament and lineament length change observed in the absence and the presence of Gorkha-Nepal earthquake (25 April 2015), from 31 January 2015 (85 days before) to 7 May 2015 (12 days after). (a) Number of lineament variation is represented by box-whisker with black line and (b) lineament mean length change (measured in kilometers) is represented by black dash line and solid black line with dot and light black arrow headed

lines showing standard deviation (SD) value, respectively based on number of days observation.

was move forward 16.6 degrees advanced from normal position.

(**Figures 9** and **10**) in the absence and the presence of earthquake event.

**3.4. Statistical analysis based on lineament data**

The unusual behavior of lineaments clearly seen from these three phases of rose diagrams which shows an anomaly prior to earthquake strike. Whereas, lineament direction was trying to reach its original state but failed to adjust its original position due to internal geodynamic activities that occurred by this high magnitude (7.8 Mw) earthquake. The mean strike position was in E-W and along with two other directions NNE-SSW and SSE-WNW were observed in the post-earthquake phase (**Figure 7e**), though still there exist anomaly compare to normal phase in the absence of earthquake event. Subsequently, all these lineaments directional change were correlated and related within the regional context of the Gorkha-Nepal and its adjoining areas which is a great indication of any structural change and considered as a vital clue to know that impending earthquake.

On the other hand, **Figure 8** illustrates the lineament directions movement around Imphal, Manipur regions from 19 March 2015 to 17 January 2016 (**Figure 8(a–e)**). In order to analyze the lineaments directional change, the present analysis has been performed in the absence

**Figure 8.** Directional change measurement through rose diagrams for Imphal-Manipur earthquake: (a) 19 March 2015, (b) 30 November 2015, (c) 16 December 2015, (d) 1 January 2016, (e) 17 January 2016 (all diagrams based on temporal lineament data).

and the presence of earthquake data. **Figure 8a** illustrates the lineament directions of normal condition in the absence of earthquake event where major lineament positions were in NNE-SSW and minor lineament positions were in SE-NW and mean strike was in NE-SW directions with 46.8 degrees – 226.79 degrees angle. **Figure 8b**, 30 November 2015 (36 days before earthquake), suggests, ESE-WSW direction and mean strike (63.4 degrees – 243.43 degrees) was move forward 16.6 degrees advanced from normal position.

**Figure 8c** represents 20 days before scenario (16 December 2015), it showed a major trend to be ESE-WNW (61.1 degrees – 241.11 degrees) with 2.3 degrees rotated back along with considering bin lengths another trend of NE-SW can also be exists. Besides those, on 1 January 2016 (prior to 4 days of earthquake events) two major trends NE-SW (61.7 degrees to 241.65 degrees) and ESE-WSW were identified by interpreting the lineament data (**Figure 8d**). Finally, **Figure 8e** represents the post-earthquake lineament direction (13 days after earthquake) which showed NE-SW (57.8 degrees – 237.83 degrees) from its immediate mean strike position data.
